Silicon composite cluster and carbon composite thereof, and electrode, lithium battery, and electronic device each including the same

ABSTRACT

A porous silicon composite includes: a porous core including a porous silicon composite secondary particle; and a shell disposed on a surface of the porous core and surrounding the porous core, wherein the porous silicon composite secondary particle includes an aggregate of silicon composite primary particles, each including silicon, a silicon suboxide on a surface of the silicon, and a first graphene on a surface of the silicon suboxide, wherein the shell include a second graphene, and at least one of the first graphene and the second graphene includes at least one element selected from nitrogen, phosphorus, and sulfur.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2018-0000905, filed on Jan. 3, 2018, and 10-2018-159039 filed on Dec.11, 2018, in the Korean Intellectual Property Office, the disclosure ofwhich is incorporated herein in its entirety by reference.

BACKGROUND 1. Field

The present disclosure relates to a silicon-containing composite, acarbon composite including the silicon-containing composite, and anelectrode, a lithium battery, and an electronic device, each includingthe porous silicon composite cluster.

2. Description of the Related Art

Silicon, has a theoretical capacity of 4,200 milliampere hours per gram(mAh/g) and a relatively low cost, and thus has been considered for useas a negative electrode material in a lithium ion battery. However,silicon may undergo a large volume expansion due to the generation of aLi_(4.4)Si alloy during discharge of a battery, and thus produce anelectrically isolated active material in the electrode. Furthermore, anincrease in the specific surface area of the active material mayaccelerate an electrolyte decomposition reaction. Therefore, it would bebeneficial to develop a structure capable of suppressing the volumetricexpansion of silicon and subsequent pulverization of the silicon.

SUMMARY

Provided is a silicon-containing composite.

Provided is a carbon composite including the silicon-containingcomposite and a carbonaceous material.

Provided is an electrode including the silicon-containing composite orthe carbon composite.

Provided is a lithium battery including an electrode that includes thesilicon-containing composite or that includes a carbon compositeincluding the silicon-containing composite and a carbonaceous material.

Provided is a field emission device including the silicon-containingcomposite or including a carbon composite including thesilicon-containing composite and a carbonaceous material.

Provided is a biosensor including the silicon-containing composite orincluding a carbon composite including the silicon-containing compositeand the carbonaceous material.

Provided is a semiconductor device including the silicon-containingcomposite or including a carbon composite including thesilicon-containing composite and the carbonaceous material.

Provided is a thermoelectric device including the silicon-containingcomposite or including a carbon composite including thesilicon-containing composite and the carbonaceous material.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect of an embodiment, a silicon-containing compositeincludes: a porous core including a porous silicon composite secondaryparticle; and a shell on a surface of the porous core and surroundingthe porous core,

wherein the porous silicon composite secondary particle includes anaggregate of silicon composite primary particles, each including

-   -   silicon,    -   a silicon suboxide on a surface of the silicon, and    -   a first graphene on a surface of the silicon suboxide,

wherein the shell includes a second graphene, and

wherein at least one of the first graphene and the second grapheneincludes at least one element selected from nitrogen (N), phosphorus(P), and sulfur (S).

According to an aspect of another embodiment, a method of preparing aporous silicon composite includes:

providing a porous silicon secondary particle;

supplying at least one of a nitrogen precursor, a phosphorus precursor,or a sulfur precursor, and a carbon source gas to the porous siliconsecondary particle; and

thermally treating the porous silicon secondary particle to prepare theporous silicon-containing composite.

According to an aspect of another embodiment, a carbon compositeincludes the porous silicon composite and a carbonaceous material.

According to an aspect of another embodiment, an electrode includes theporous silicon composite, the carbon composite, or a combinationthereof.

According to an aspect of another embodiment, a lithium battery includesthe electrode, which includes the silicon-containing composite, thecarbon composite, or a combination thereof.

According to an aspect of another embodiment, an electronic deviceincludes the silicon-containing composite, the carbon composite, or thecombination thereof.

The electronic device may be a field emission device, a biosensor, asemiconductor device, or a thermoelectric device.

According to an aspect of another embodiment, a silicon-containingcomposite includes:

a core including a porous silicon composite secondary particle; and

a shell on and surrounding the core,

wherein the porous silicon composite secondary particle includes anaggregate of silicon composite primary particles,

the silicon composite primary particles each include

-   -   a silicon suboxide,    -   a thermal treatment product of the silicon suboxide; and    -   a first graphene on a surface of the silicon suboxide, the        thermal treatment product of the silicon suboxide, or the        combination thereof.

wherein the shell comprises a second graphene, and at least one of thefirst graphene and the second graphene comprises at least one elementselected from nitrogen (N), phosphorus (P), and sulfur (S).

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1A is a schematic view illustrating a structure of asilicon-containing composite according to an embodiment;

FIG. 1B is a schematic view that illustrating a structure of asilicon-containing composite according to another embodiment;

FIG. 1C is a diagram illustrating a method of stacking graphene onsilicon, which includes a silicon suboxide on its surface, in asilicon-containing composite according to an embodiment;

FIG. 2 is a diagram illustrating an embodiment of a method of dopingnitrogen in a silicon-containing composite;

FIG. 3 is a diagram illustrating an embodiment of a method of preparinga silicon-containing composite;

FIG. 4 is a graph of intensity (arbitrary units, a.u.) versus Ramanshift (per centimeter, cm⁻¹), which shows the results of Ramanspectroscopic analysis with respect to the porous silicon compositeprepared according to Preparation Example 1;

FIG. 5 is a graph of weight percent (%) versus temperature (° C.), whichshows the results of thermogravimetric analysis for the poroussilicon-containing composites prepared according to Preparation Example1 and Reference Example 1;

FIGS. 6 to 8 are graphs of intensity versus binding energy (electronvolts, eV), which show the results of X-ray photoelectron spectroscopicanalysis for the porous silicon composite prepared according toPreparation Example 1;

FIGS. 9A and 9B are scanning electron microscope (SEM) images of thesilicon-containing composite prepared according to Preparation Example1;

FIGS. 10A and 10B are SEM images of the silicon-containing compositeprepared according to Reference Example 1;

FIGS. 11A and 11B are transmission electron microscope (TEM) images ofthe silicon-containing composite prepared according to PreparationExample 1;

FIG. 12A is a diagram illustrating an embodiment of a lithium battery;

FIG. 12B is a perspective view of an embodiment of a thermoelectricmodule;

FIG. 12C is a schematic view illustrating an embodiment of athermoelectric cooler having a design using the Peltier effect;

FIG. 12D is a schematic view illustrating an embodiment of athermoelectric generator having a design using the Seebeck effect; and

FIG. 12E is a cross-sectional view illustrating a structure of anembodiment of an electrode of a biosensor.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of at least onesilicon-containing composite, an electrode including an electrode activematerial containing the silicon-containing composite, and a lithiumbattery, a field emission device, a biosensor, and a semiconductordevice each including the silicon-containing composite, examples ofwhich are illustrated in the accompanying drawings, wherein likereference numerals refer to like elements throughout. In this regard,the present embodiments may have different forms and should not beconstrued as being limited to the descriptions set forth herein.Accordingly, the embodiments are merely described below, by referring tothe figures, to explain aspects.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

As used herein, the singular forms includes any and all combinations toinclude the plural forms, including s, including s, including s of oneor more of the associated list to include the plural forms, includes anyand all combinations used herein. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. Expressions such as “at least one of,” when preceding alist of elements, modify the entire list of elements and do not modifythe individual elements of the list. It will be further understood thatthe terms “comprises” and/or “comprising,” or “includes” and/or“including” when used in this specification, specify the presence ofstated features, regions, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, regions, integers, steps, operations, elements,components, and/or groups thereof.

Spatially relative terms describe one element or feature's relationshipto another element(s) or feature(s) as illustrated in the figures. Itwill be understood that the spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if thedevice in the figures is turned over, elements described as “below” or“beneath” other elements or features would then be oriented “above” theother elements or features. Thus, the exemplary term “below” canencompass both an orientation of above and below. The device may beotherwise oriented (rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein interpreted accordingly.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within +20%, 10% or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

The formation of a coating layer of, for example, carbon on surfaces ofthe silicon, has been suggested as a way to address the volumetricexpansion of silicon and the subsequent pulverization which occur duringdischarging of a battery. However, currently available silicon materialsare still not satisfactory in terms of their ability to effectivelyminimize volumetric expansion and improve charging and dischargingefficiency of batteries

According to an aspect, a silicon-containing composite includes: aporous core including a porous silicon composite secondary particle; anda shell on a surface of the porous core and surrounding the porous core,the shell including a second graphene,

wherein the porous silicon composite secondary particle includes anaggregate of silicon composite primary particles, each includingsilicon,

-   -   a silicon suboxide on at least one surface of the silicon, and    -   a first graphene on a surface of the silicon suboxide,    -   wherein the shell includes a second graphene,    -   wherein at least one of the first graphene and the second        graphene includes at least one element selected from nitrogen        (N), phosphorus (P), and sulfur (S),

The silicon-containing composite may be porous.

The silicon suboxide may be present in a form of a film, a matrix, or acombination thereof. Also, the first graphene and the second grapheneare each independently in a form of a film, a particle, a matrix, or acombination thereof.

The term “matrix” represents a three-dimensional space and the term“membrane” represents a two-dimensional space compared to a matrix.

In various embodiments, the second graphene may be epitaxially grown ona surface of the silicon suboxide of the porous silicon compositesecondary particle

In an embodiment, the first graphene may be epitaxially grown from thesurface of the silicon suboxide, and the second graphene may beepitaxially grown from the surface of the porous silicon compositesecondary particle.

The silicon-containing composite may be porous. As used herein, the term“cluster” refers to an aggregate of two or more primary particles, andmay be construed as having substantially the same meaning as a“secondary particle.”

As used herein, the term “graphene” refers to a structure having theform of a flake, a nanosheet, or a layer (e.g., film), wherein thenanosheet may refer to a structure disposed in an irregular manner on asurface of silicon suboxide or on a surface of the porous siliconcomposite secondary particle, and the layer may refer to a structuredisposed as a continuous and uniform film of graphene on a siliconsuboxide or on the porous silicon secondary particle. As such, thegraphene may have a structure including distinct layers or a structurewithout any distinct layers.

As used herein, the term “silicon suboxide” refers to a compound of theFormula SiOx, wherein 0<x<2.

As used herein, the term “silicon su—boxide-like” refers to a mixture ofcompounds that may include at least one of Si and SiO₂, so as to have anaverage composition represented by the Formula SiOx, wherein 0<x<2.

In an embodiment, the core of the silicon-containing composite may havea size of about 3 micrometers (μm) to about 10 μm, or about 3 μm toabout 9 μm, or about 5 μm to about 10 μm, and the shell may have athickness of about 10 nanometers (nm) to about 5,000 nm, or about 10 nmto about 2500 nm, and in another embodiment, about 10 nm to about 1,000nm. Here, the size means either the diameter of the length of the majoraxis.

FIG. 1A illustrates a silicon-containing composite 11 according to anembodiment.

Referring to FIG. 1A, the silicon-containing composite 11 includes acore 1 including a porous silicon composite secondary particle and ashell 2 disposed on and surrounding the core 2, the shell including asecond graphene 10 b.

The porous silicon composite secondary particle may include an aggregateof silicon composite primary particles 10, and the silicon compositeprimary particle may include silicon, a silicon suboxide of the FormulaSiOx (wherein 0<x<2), on a surface of the silicon, and a first graphene10 a on a surface of the silicon suboxide. In the silicon compositeprimary particle, the first graphene may form a shell on a surface ofthe silicon suboxide, and in the silicon composite secondary particle,the second graphene may form a shell on a surface of the core, resultingin a core/shell structure of the porous silicon composite cluster. Sucha core/shell structure may suppress volume expansion of the siliconprimary particles and inhibit side reactions that may occur with anelectrolyte. Thus the silicon-containing composite comprises a firstcore/shell structure and a second core/shell structure, in which thefirst core/shell structure includes the porous core comprising theporous silicon composite secondary particle and the shell comprising thesecond graphene on the surface of the porous core, and the secondcore/shell structure comprises a core comprising the silicon and thesilicon suboxide on a surface of the silicon, and the shell comprisesthe first graphene on a surface of the silicon suboxide.

The first graphene 10 a may include a plurality of graphene layers. Thenumber of graphene layers included in the first graphene 10 a of thecore 1 may be the same as or different from the number of graphenelayers included in the second graphene 10 b of the shell 2.

In an embodiment, the second graphene 10 b of the shell 2 may have adensity which is greater than the density of the first graphene 10 a ofthe core 1. In one another embodiment, the number of graphene layersincluded in the first graphene 10 a of the core 1 may be an integer ofabout 1 to about 30, or about 2 to about 20, or in another embodiment,about 5 to about 15, and in still another embodiment, about 10. Thenumber of graphene layers included in the second graphene 10 b of theshell 2 may be an integer of about 1 to about 50, or about 10 to about40, or in another embodiment, about 20 to about 30.

In an embodiment, the first graphene 10 a and the second graphene 10 bmay each be doped with at least one element (dopant) selected fromnitrogen (N), phosphorus (P), and sulfur (S).

In an embodiment, an amount of at least one element selected from N, P,and S in the silicon-containing composite may be about 0.2 atomicpercent (atomic %) or less, or about 0.1 atomic % or less, or about 0.08atomic % or less, and in another embodiment, about 0.05 atomic % toabout 0.2 atomic %, or about 0.08 atomic % to about 0.2 atomic %, orabout 0.1 atomic % to about 0.2 atomic %, at a surface depth of about 10nm or less, as measured by X-ray photoelectron spectroscopy (XPS)analysis. Here, the surface depth may be from about 1 nm to about 10 nm,or about 2 nm to about 10 nm, or for example, about 5 nm to about 10 nm.

In an embodiment, an amount of the at least one element selected from N,P, and S may be from about 2,000 parts per million (ppm) or less, orabout 1,500 ppm or less, or about 1,000 ppm or less, and in anotherembodiment, about 50 ppm to about 2,000 ppm, and in still anotherembodiment, about 500 ppm to about 2,000 ppm.

FIG. 1B illustrates a porous silicon composite 11 according to anotherembodiment.

Referring to FIG. 1B, the silicon-containing composite 11 includes astructure in which a carbonaceous coating layer 12 is additionallydisposed on the surface of the porous silicon composite 11 of FIG. 1A.The carbonaceous coating layer 12 may include amorphous carbon,crystalline carbon, or a combination thereof. The carbonaceous coatinglayer may also include at least one element selected from N, P, and S,in the same manner as in the first graphene 10 a and the second graphene10 b.

In an embodiment, the at least one element selected from N, P, and S maynot be included in the first graphene and the second graphene of theporous silicon composite 11, but may be included only in thecarbonaceous coating layer of the porous silicon composite 11.

The effect of the case in which N is included in the silicon-containingcomposite will now be described with reference to FIG. 2 .

Without being limited by theory, it is understood that during thepreparation of the silicon-containing composite cluster, the graphenemay include a defective region 25 and consequently may have poorconductivity. When such graphene is used as an electrode material, asolid electrolyte interphase (SEI) layer may be more easily formed. Asshown in FIG. 2 , when N is included and incorporated into a defectiveregion 25 of graphene, the stability and quality of graphene may befurther improved. Here, N may be introduced to a pyridinic N position22, a quaternary N position 24, a pyrrolic N position 26, and the like,thereby further improving the quality of graphene.

In addition, when N is introduced to a defective region 25 of thegraphene, an electrode material including such a structure mayefficiently suppress the formation of the SEI layer.

In addition, when N is introduced to a defective region 20 of thegraphene, an electrode material including such a structure mayefficiently suppress the formation of the SEI layer.

In an embodiment, the silicon-containing composite may further includean outer layer having a density greater than the density of the core 1.The outer layer may have a thickness of about 20 nm to about 60 nm, orabout 20 nm to about 50 nm, or about 30 nm to about 40 nm. However,embodiments are not limited thereto.

In an embodiment, an intensity ratio of peak D to peak G (Id/Ig) in thesilicon-containing composite may be from about 0.8 to about 1.5, inanother embodiment, about 1 to about 1.4, in still another embodiment,about 1.1 to about 1.3 (for example, about 1.2), as measured by Ramanspectroscopy analysis.

In an embodiment, a 20% weight loss temperature of thesilicon-containing composite may be greater than a 20% weight losstemperature of a silicon-containing composite not including the at leastone elements selected from N, P, and S, as measured by thermogravimetricanalysis. For example, a 20% weight loss temperature of thesilicon-containing composite may be about 7° C. to 15° C. greater than a20% weight loss temperature of a silicon-containing composite which doesnot comprise the at least one element selected from nitrogen,phosphorous, and sulfur as measured by thermogravimetric analysis.

When the silicon-containing composite does not include N, the 20% weightloss temperature may be, for example, about 710° C. to about 730° C.

The core and the shell of the silicon-containing composite may eachfurther include graphite.

The ratio of the diameter of the porous silicon composite secondaryparticle to the diameter of the silicon-containing composite 11 may befrom about 1:1 to about 1:30, and in another embodiment, about 1:1 toabout 1:25, or about 1:1 to about 1:22, and in still another embodiment,about 1:21. The ratio of the diameter of the porous silicon compositesecondary particle to the silicon-containing composite may be a diameterratio when the porous silicon composite secondary particle and theporous silicon composite 11 both have a spherical shape. When the poroussilicon composite secondary particle and the silicon-containingcomposite are both non-spherical in shape, the diameter ratio refers toa length ratio of the major axis.

In another embodiment, the core of the silicon-containing composite 11may have a diameter of about 3 micrometers (μm) to about 10 μm, or about3 μm to about 9 μm, or about 2.5 μm to about 7.5 μm. The thickness ofthe shell of the silicon-containing composite may be about 10 nanometer(nm) to about 5,000 nm (i.e., about 0.01 μm to about 5 μm), or about 10nm to about 2,500 nm, for example, about 10 nm to about 1,000 nm. Theratio of the diameter of the core 1 to the thickness of the shell 2(e.g., a carbon coating layer) of the porous silicon composite 11 may befrom about 1:0.001 to about 1:1.67, or about 1:0.005 to about 1:1.67 orabout 1:0.0033 to about 1:1.67, and may be, for example, about 1:0.001,about 1:0.0033, about 1:0.5, or about 1:1.67.

The total amount of the first graphene and the second graphene in thesilicon-containing composite may be from about 0.1 parts by weight toabout 2,000 parts by weight, and in an embodiment, about 0.1 parts byweight to about 300 parts by weight, and in another embodiment, about0.1 parts by weight to about 90 parts by weight, an in still anotherembodiment, about 5 parts by weight to about 30 parts by weight, basedon 100 parts by weight of the silicon. When the total amount of thefirst graphene and the second graphene is within these ranges, volumeexpansion of the silicon of the porous silicon composite may beeffectively suppressed, and improved conductivity of the porous siliconcomposite may be obtained.

In the silicon composite primary particle, the first graphene may bespaced apart from a surface of the silicon suboxide having the FormulaSiOx (wherein 0<x<2), by a distance of about 10 nm or less, or about 8nm or less, or about 5 nm or less. The first graphene may include atleast 1 to 30 graphene layers, or about 1 to 25 graphene layers, orabout 1 to about 20 graphene layers, and may have a total thickness ofabout 0.3 nanometers to about 1000 nanometers, for example, for example,about 0.3 nm to about 50 nm, for example, about 0.6 nm to about 50 nm,for example, about 1 nm to about 30 nm. The first graphene may beoriented at an angle of about 0° to about 90° with respect to a majoraxis of the silicon. Here, the major axis refers to a Y-axis.

As shown in FIG. 1C, the first graphene and the second graphene 10 a,10b may be oriented on the surface of the silicon oxide at an angle Θ ofabout 90° with respect to a major axis (i.e., Y-axis) of the plate-likeand needle-like silicon composite primary particles 10, and may bedirectly on the surface of the silicon suboxide.

In the silicon-containing composite, the second graphene may extend froma surface of the silicon suboxide by a distance of about 1,000 nm orless, for example, about 500 nm or less, and in an embodiment, about 10nm or less, and in an embodiment, about 1 nm or less, and in anotherembodiment, about 0.00001 nm to about 1 nm. The second graphene mayinclude about 1 to about 30, or about 1 to about 25, or about 1 to about20 graphene layers. In the silicon-containing composite, the secondgraphene may have a total thickness of about 0.6 nm to about 50 nm, orabout 0.8 nm to about 50 nm, or in an embodiment, about 1 nm to about 50nm, and may be oriented at an angle of about 0° to about 90° withrespect to a major axis of the silicon.

The silicon suboxide having the Formula SiOx (wherein 0<x<2), may have athickness of about 30 μm or less, or about 1 μm or less, or about 100 nmor less, and for example, about 10 nm.

The shape of the silicon is not limited to any specific form, and may bein the form of, for example, a sphere, a nanowire, a needle, a rod, or acombination thereof. The silicon may have an average diameter of about10 nm to about 40 μm, or about 20 nm to about 10 μm, or about 50 nm toabout 1 μm, for example about 100 nm.

The porous silicon composite secondary particle may have an averageparticle diameter (D50) of about 200 nm to about 50 μm, and in anembodiment, about 1 μm to about 30 μm, and in another embodiment, about1 μm to about 10 μm, and in still another embodiment, about 3 μm toabout 5 μm. The porous silicon composite secondary particle may have aspecific surface area of about 0.1 square meters per gram (m²/g) toabout 100 m²/g, or about 1 m²/g to about 50 m²/g, and in an embodiment,about 1 m²/g to about 30 m²/g. The porous silicon composite secondaryparticle may have a density of about 0.1 grams per cubic centimeter(g/cc) to about 2.8 g/cc, for example, about 0.5 g/cc to about 2 g/CC.

The silicon-containing composite may further include a carbonaceouscoating layer on a surface thereof, the carbonaceous coating layerincluding an amorphous carbon. When the silicon-containing compositeincludes a carbonaceous coating layer, a lithium battery including thesilicon-containing composite may have improved lifetime characteristics,though initial efficiency may be reduced.

In the same manner as the first graphene and the second graphene, thecarbonaceous coating layer may also include at least one elementselected from N, P, and S. A method of including the at least oneelement selected from N, P, and S in the carbonaceous coating layer maybe applicable in various ways.

The carbonaceous coating layer may have a thickness of, for example,about 10 nm to about 5,000 nm, or about 10 nm to about 3,000 nm, orabout 20 nm to about 1,500 nm.

The amorphous carbon may include pitch carbon, soft carbon, hard carbon,mesophase carbon pitch carbide, sintered coke, carbon fiber, or acombination thereof.

The carbonaceous coating layer including amorphous carbon may furtherinclude a crystalline carbon, and the crystalline carbon may include afullerene, natural graphite, artificial graphite, graphene, a carbonnanotube, or a combination thereof.

The carbonaceous coating layer may be a non-porous continuous coatinglayer, and may have a thickness of about 1 nm to about 5,000 nm, orabout 5 nm to about 2,500 nm, or about 10 nm to about 1,000 nm. Thecarbonaceous coating layer may include, for example, a firstcarbonaceous coating layer, which includes the amorphous carbon, and asecond carbonaceous coating layer, which includes the crystallinecarbon.

The silicon-containing composite may have a narrow particle sizedistribution. For example, the silicon-containing composite may have aD50 particle size of about 1 μm to about 30 μm, a D10 particle size ofabout 0.001 μm to about 10 μm, and a D90 particle size of about 10 μm toabout 30 μm. As used herein, the term “D50 particle size” refers to aparticle diameter corresponding to 50% of the particles in a cumulativedistribution curve in which particles are accumulated in the order ofparticle diameter from the smallest particle to the largest particle anda total number of accumulated particles is 100%. Similarly, the terms“D10” and “D90” respectively indicate particle diameters correspondingto 10%, and 90% of the particles in the cumulative distribution curve ofthe porous silicon secondary particle, respectively.

The silicon-containing composite according to an embodiment may have anarrow particle size distribution within these ranges. Unlike thesilicon-containing composite according to an embodiment, siliconcomposite secondary particles, which are aggregates of silicon compositeprimary particles, may have an irregular secondary particle sizedistribution, and thus it may be difficult to control the particle sizedistribution of the negative active material so as to improve the cellperformance.

The amount of oxygen atoms in the porous silicon composite may be fromabout 0.01 atomic % to about 15 atomic %, and in an embodiment, about3.5 atomic % to about 5 atomic %, and in another embodiment, about 3.5atomic % to about 3.8 atomic %. Without being limited by theory, it isunderstood that the advantages associated with such a small amount ofoxygen in the porous silicon composite cluster, as compared with that ofconventional silicon-based materials, are attributed to the suppressedoxidation of silicon due to the use of a dispersing agent (e.g., stearicacid) in preparing the porous silicon composite cluster. Such a reducedamount of oxygen in the silicon-containing composite may improve siliconcapacity and initial efficiency.

The production of conventional graphene-grown silicon primary particles,a negative electrode including the conventional graphene-grown siliconprimary particles, and the state of the negative electrode aftercharging and discharging, will now be described. The conventionalgraphene-grown silicon primary particles including graphene directlygrown on silicon particles have a structure including a first grapheneon needle-like silicon particles. A negative electrode may bemanufactured by forming a negative active material layer including amixture of the conventional graphene-grown silicon primary particles andgraphite on a copper current collector.

After charging and discharging of the negative electrode, due to thevolume expansion and contraction of silicon, the graphene-grown siliconprimary particles acting as an active material may become separated, andconsequently, isolation of the silicon may occur, leading to reducedcapacity. Furthermore, continuous growth of a solid electrolyteinterphase (SEI) layer on the surface of the silicon primary particlesmay also occur, leading to increased lithium consumption and reduceddurability against charging and discharging.

The inventors have advantageously discovered that a negative electrodehaving improved durability over multiple charging and discharging cyclesmay be obtained by using a silicon-containing composite having a doublecore/shell structure. Without being limited by theory, it is believedthat the double core/shell structure may form a uniform charging anddischarging network that suppresses disintegration caused by the volumeexpansion and contraction of silicon during charging and discharging,and which may ensure formation of a stable SEI layer on the surface ofthe porous silicon composite cluster.

In addition, silicon having a diameter of about 100 nm or more, forexample, about 150 nm or more, and for example, about 100 nm to about200 nm may be used for preparing a silicon-containing compositeincluding doped (e.g., N-doped) graphene on a silicon/silicon suboxide.

The silicon-containing composite according to an embodiment may haveexcellent capacity characteristics with a capacity range of about 600milliampere hours per cubic centimeter (mAh/cc) to about 2,000 mAh/cc,or about 750 mAh/cc to about 2,000 mAh/cc, or about 1,000 mAh/cc toabout 2,000 mAh/cc.

According to another aspect, a silicon-containing composite includes: acore including a porous silicon composite secondary particle; and ashell disposed on and surrounding the core,

wherein the porous silicon composite secondary particle includes anaggregate of silicon composite primary particles, each including

-   -   a silicon suboxide, a thermal treatment product of the silicon        suboxide, or a combination thereof; and    -   a first graphene disposed on a surface of the silicon suboxide,        the thermal treatment product of the silicon suboxide, or the        combination thereof, and

wherein the shell includes a second graphene, and at least one of thefirst graphene and the second graphene includes at least one elementselected from N, P, and S.

As used herein, the term “thermal treatment product of a siliconsuboxide” refers to a product obtained by thermally treating the siliconsuboxide having the Formula SiOx (wherein 0<x<2). The thermal treatmentmay be a thermal treatment capable of facilitating the growth ofgraphene on the surface of the silicon suboxide. In an embodiment, thethermal treatment include a vapor deposition reaction, in which a gasincluding a carbon source gas or a mixture of a carbon source gas and areducing gas may be used as the graphene source. For example, thereducing gas may be hydrogen.

The thermal treatment product of the silicon suboxide having the FormulaSiOx (wherein 0<x<2), may be a product obtained by thermally treatingthe silicon suboxide in an atmosphere including a carbon source gas or acombination of a carbon source gas and a reducing gas.

The thermal treatment product of the silicon suboxide having the FormulaSiOx (wherein 0<x<2) may have, for example, a structure includingsilicon (Si) arranged in a matrix of a silicon oxide of the FormulaSiO_(y) (wherein 0<y≤2).

In an embodiment, the thermal treatment product of the silicon suboxideof the Formula SiOx (wherein 0<x<2) may have, for example, i) astructure including silicon (Si) arranged in a matrix of SiO₂, ii) astructure including silicon (Si) arranged in a matrix including SiO₂ andSiO_(x) (wherein 0<x<2), or iii) a structure including silicon (Si)arranged in a matrix of SiO_(y) (wherein 0<y<2). Put another way, thethermal reaction product of the silicon suboxide includes silicon in amatrix comprising SiO₂, SiO_(y), wherein 0<y<2, or a combinationthereof.

In an embodiment, an amorphous carbon layer may be between the firstgraphene and the silicon suboxide, the thermal treatment product of thesilicon suboxide, or the combination thereof. In another embodiment, anamorphous carbon layer may be between the second graphene and the coreincluding the porous silicon composite secondary particle. The amorphouscarbon layer may serve as a graphene-growing nucleus facilitating thegrowth of graphene on the surface of the silicon suboxide and thesurface of the core.

In an embodiment, a carbide such as a silicon carbide (SiC) is notpresent between the silicon and the silicon suboxide and/or between thesilicon suboxide and the graphene. A carbide, for example a siliconcarbide, does not react with lithium so that, when used as an electrodematerial, an electrode may have a reduced capacity. In addition, inorder to form graphene on a surface of the silicon carbide, a hightemperature is required, resulting in increased crystallinity of thesilicon and accordingly, an accelerated pulverization phenomenon duringcharging and discharging of lithium.

An embodiment of a method of preparing a porous silicon compositeaccording to one of the above-described embodiments will now bedescribed with reference to FIG. 3 .

First, a structure including silicon and a silicon suboxide having theFormula SiOx (wherein 0<x<2) on a surface of the silicon may bedisintegrated to obtain a disintegrated silicon primary particle.

The disintegrated silicon primary particle may be mixed with adispersing agent and a solvent to thereby obtain a composition 30. Next,a porous silicon composite secondary particle 31 may be prepared fromthe composition 30 by, for example, spray drying the composition 30.

The porous silicon composite secondary particle 31 may have a porosityof, for example, about 0.1% to about 50%, and a pore size of, forexample, about 10 nm to about 500 nm. As used herein, the term“porosity” is used to refer to a measure of the empty space (voids orpores) in a material and is determined as a percentage of the volume ofvoids in a material based on the total volume of the material.

The preparing of the porous silicon secondary particle 31 from thecomposition 30 may be performed by any suitable method, for example,co-precipitation, spray drying, or a solid phase method. For example,the porous silicon composite secondary particle may be prepared by spraydrying. When the porous silicon composite secondary particle 31 isprepared by spray drying, a particle diameter may be controlled byappropriately choosing a spraying type, a pressurized gas supply rate, acomposition supply rate, a drying temperature, and the like.

In an embodiment, the spray drying may be performed at an atmospherictemperature of about room temperature (25° C.) to about 500° C., forexample, about 50° C. to about 300° C. When the spray drying isperformed within these temperature ranges, particle agglomeration andblocking of a particle discharge outlet may be prevented, due tomoisture condensation near the particle discharge outlet, and the poroussilicon composite secondary particles may have appropriate porosity.

In the spray drying, a spraying pressure may be about 1 bar to about 5bar.

Prior to the spray drying, a surface area of the silicon primaryparticle 31 may be increased, for example, by pulverization. To thisend, pulverized silicon primary particles may be used as the startingmaterial.

For example, when formed by spray drying, the obtained porous siliconcomposite secondary particles 31 may be spherical in shape. A dispersingagent, for example, stearic acid, may partially remain on a portion of asurface of the porous silicon secondary particle 31. The spray dryingnozzle size is about 50 μm to about 1,000 μm, for example, about 150 μm.

Afterwards, while a carbon source gas and at least one precursorselected from a N precursor, a P precursor, and a S precursor aresupplied to the porous silicon secondary particle 31, the porous siliconcomposite secondary particle 31 may be thermally treated to therebyprepare the porous silicon composite 21. In FIG. 3 , reference numeral10 a denotes a first graphene, reference numeral 10 b denotes a secondgraphene, and a reference 20 represents a silicon composite primaryparticle. As such, the at least one of the N precursor, the P precursor,and the S precursor may be provided to the porous silicon compositesecondary particle using the existing carbon source gas. In this regard,the preparation process of the target product may be simplified andeasy. A mixing ratio of the at least one precursor selected from the Nprecursor, the P precursor, and the S precursor to the carbon source gasmay be controlled by adjusting the volume of each precursor and thevolume of the carbon source gas.

In an embodiment, an amount of the at least one precursor selected fromthe N precursor, the P precursor, and the S precursor may be about 20volume % or less, or about 15 volume % or less, or about 10 volumepercent or less, for example, about 5 volume % to about 20 volume %, orabout 5 volume % to about 15 volume %, or about 5 volume % to about 10volume %, based on the total amount of the reaction gas. When the amountof the at least one precursor selected from the N precursor, the Pprecursor, and the S precursor is within these ranges, the crystallinityand quality of graphene may be excellent.

The carbon source gas may fill the pores in the porous silicon compositesecondary particles and then carbon grows on surfaces of the siliconcomposite secondary particles.

The solvent may include an alcohol, for example, ethanol, methanol, orisopropyl alcohol, or a combination thereof. When these alcoholicsolvents are used, the dispersing agent may be removed as the solvent isremoved, so that the amount of the dispersing agent remaining in thesilicon-containing composite may be reduced. As a result, an amount ofoxygen may be reduced in the silicon-containing composite and thus onlya small amount of oxygen may remain.

The dispersing agent may uniformly disperse the silicon primaryparticles. The dispersing agent may include, but is not limited to,stearic acid, resorcinol, polyvinyl alcohol, pitch, or a combinationthereof. An amount of the dispersing agent may be about 1 part by weightto about 15 parts by weight, or about 2.5 parts by weight to about 12parts by weight, for example, about 5 parts by weight to about 10 partsby weight, based on 100 parts of a total weight of the composition. Whenthe amount of the dispersing agent is within these ranges, silicon andgraphene may be uniformly dispersed without agglomerating.

The carbon source gas may include a compound represented by Formula 1, acompound represented by Formula 2, an oxygen-containing gas representedby Formula 3, or a combination thereof:C_(n)H_((2n+2−a))[OH]_(a)  [Formula 1]

wherein, in Formula 1, n may be an integer of 1 to 20, and a may be 0 or1,C_(n)H_((2n))  [Formula 2]

wherein, in Formula 2, n may be an integer of 2 to 6,CxHyOz  [Formula 3]

wherein, in Formula 3, x may be 0 or an integer of 1 to 20, y may be 0or an integer of 1 to 20, and z may be 1 or 2.

The carbon source gas may include, for example, methane, ethylene,propylene, methanol, ethanol, propanol, or a combination thereof.

The thermal treatment may be performed at a temperature of about 600° C.to about 1,100° C., or about 650° C. to about 1,000° C., and in anembodiment, about 700° C. to about 1,000° C. When the thermal treatmentis performed within these temperature ranges, graphene may be generatedat a high density in the core and shell.

As described above, the silicon composite primary particles may includesilicon, the silicon suboxide of the Formula SiO_(x) (wherein 0<x<2) ona surface of the silicon, and graphene on a surface of the siliconsuboxide. The silicon suboxide of the Formula SiOx (wherein 0<x<2) is anunstable oxygen-deficient material as compared with silicon oxide(SiO₂), and tends to form a stable material by reacting with anotherreactive material, such as a carbon source gas. Based on this tendencyof the silicon oxide, the silicon suboxide of the Formula SiO_(x)(wherein 0<x<2) may be used as a seed layer for forming graphene.

A thickness of the silicon suboxide of the Formula SiO_(x) (wherein0<x<2) disposed on the surface of the silicon may affect a shape and/ora structure of the graphene. The silicon suboxide has a layer form.

The thickness of the silicon suboxide (SiO_(x), wherein 0<x<2) film maybe determined by controlling a process involved in graphene formation,for example, by controlling the composition of the carbon source gasused to form the graphene. The thickness of the silicon suboxide(SiO_(x), wherein 0<x<2) film may be about 300 μm or less, or about 250μm or less, or about 150 μm or less.

In an embodiment, the silicon suboxide (SiO_(x), wherein 0<x<2) film inthe silicon-containing composite for use in a battery may have athickness of about 10 nm or less, and in another embodiment, about 0.1nm to about 10 nm, or about 0.1 nm to about 7.5 nm, or in still anotherembodiment, about 0.1 nm to about 5 nm. In an embodiment, the distancethickness may be for example, about 5 nm or less, for example about 1 nmor less, for example, about 0.0001_nm to 1_nm.

When the thickness of the silicon suboxide (SiO_(x), wherein 0<x<2) filmis within these ranges, a battery manufactured using thesilicon-containing composite including the silicon suboxide (SiO_(x),wherein 0<x<2) film may have improved capacity.

In an embodiment, the graphene may be formed as a coating on a surfaceof the silicon suboxide of the Formula SiOx (wherein 0<x<2) bynon-catalytic vapor carbon deposition.

The vapor carbon deposition may include thermally treating the siliconcovered with the silicon suboxide of the Formula SiO_(x) under a mixedgas atmosphere, the atmosphere including a compound represented byFormula 1, a compound represented by Formula 2, an oxygen-containing gasrepresented by Formula 3, or a combination thereof, and at least oneprecursor selected from the N precursor, the P precursor, and the Sprecursor.C_(n)H_((2n+2−a))[OH]_(a)  [Formula 1]wherein, in Formula 1, n may be an integer of 1 to 20, and a may be 0 or1,C_(n)H_((2n))  [Formula 2]

wherein, in Formula 2, n may be an integer of 2 to 6,CxHyOz  [Formula 3]

wherein, in Formula 3, x may be 0 or an integer of 1 to 20, y may be 0or an integer of 1 to 20, and z may be 1 or 2.

While not limited to this theory, it is understood that coating with thegraphene by the above-described vapor carbon deposition is associatedwith reforming of the silicon suboxide of the Formula SiOx covering thesilicon by using CO₂ in the gas mixture.

According to the vapor carbon deposition, graphene may be directly grownon the silicon which is covered with silicon suboxide of the FormulaSiOx, and thus the silicon and graphene may be strongly adhered to eachother.

In an embodiment, even when a SiO_(x) layer is not present on thesilicon, by a process of reacting a carbon-containing mixed gas and anoxygen-containing mixed gas, a SiO_(x) layer may be formed first on thesurface of the silicon by a reaction between the silicon and theoxygen-containing mixed gas, and then graphene may be formed thereon bya reaction with the carbon-containing mixed gas. Here, a degree ofadhesion between the silicon and the graphene may be evaluated bymeasuring a distance between them by using a scanning electronmicroscope (SEM)

The first graphene of the silicon composite primary particleconstituting the silicon-containing composite may be spaced apart(extend from) the silicon of the silicon suboxide by a distance of about10 nm or less, or about 5 nm or less, or about 1 nm or less, forexample, about 0.5 nm to about 10 nm, or about 0.5 nm to about 7.5 nm,or about 0.5 nm to about 5 nm. In an embodiment, the first graphene maybe spaced apart from (extend from) the silicon by a distance about 1 nmor less, or about 0.8 nm or less, or about 0.6 nm or less, for example,about 0.5 nm to about 1 nm, or about 0.5 nm to about 0.8 nm, or about0.5 nm to about 7.5 nm. The first graphene may be oriented at an angleof about 0° to about 90° with respect to a major axis of the silicon.The first graphene may include about 1 to about 20, or about 1 to about15, or about 1 to about 10 graphene layers, and may have a totalthickness of about 0.6 nm to about 12 nm, or about 1 nm to about 10 nm,or about 1 nm to about 7.5 nm. The first graphene may be oriented at anangle of 0° to about 90° with respect to the major axis of the silicon.

The shape of the silicon may not be limited to any specific shape and,for example, may have the form of a sphere, a nanowire, a needle, a rod,a particle, a nanotube, a nanorod, a wafer, a nanoribbon, or acombination thereof.

In an embodiment, the silicon may be in the form of needle-likeparticles. For example, the needle-like silicon particles may have alength of about 100 nm to about 160 nm, or about 105 nm to about 150 nm,and in some embodiments, about 108 nm to about 125 nm; and may have athickness of about 10 nm to about 100 nm, or about 15 nm to about 75 nm,and in some embodiments, about 20 nm to about 50 nm, and in some otherembodiments, about 40 nm.

In an embodiment, the silicon suboxide (SiO_(x), wherein 0<x<2) film maybe formed on a surface of silicon having a needle-like shape, and thegraphene may be formed on a surface of the silicon suboxide.

In another embodiment, the silicon suboxide (SiO_(x), wherein 0<x<2) maybe formed on silicon nanoparticles, and the graphene may be formed onthe silicon suboxide. The silicon nanoparticles may have an averageparticle diameter of about 40 nm to about 40 μm, or about 40 nm to about1 μm, for example, about 40 nm to about 100 nm.

When the silicon has a form of a wafer, the silicon wafer may have athickness of about 2 mm or less, or about 1 mm or less, or about 0.5 mmor less, or about 0.1 mm or less, for example, about 0.001 mm to about 2mm, or about 0.001 mm to about 1 mm, or about 0.005 mm to about 0.5 mm.

The graphene is a polycyclic aromatic molecule comprising a plurality ofcarbon atoms covalently bonded to one another. The covalently bondedplurality of carbon atoms form a 6-membered ring as a basic repeatingunit, but a 5-membered ring and/or a 7-membered ring may be included inthe graphene. Accordingly, the graphene may be a single layer of thecovalently bonded carbon atoms (in general, having a sp² bond).

The graphene may include a single layer or a plurality of layers stackedupon one another, for example, one layer to about 100 layers, about 2layers to about 100 layers, or about 3 layers to about 50 layers.

The graphene may have a structure of a nanosheet, a layer (or film), aflake, or a combination thereof. The term “nanosheet” refers to amaterial having a two-dimensional structure in the form of a sheethaving a thickness of less than about 1000 nanometers (nm), or athickness in a range of about 1 nm to about 1000 nm, and which isdisposed in an irregular manner on the silicon suboxide or on the poroussilicon secondary composite particle. As used herein, the term “layer”“film” refers to a continuous, uniform layered structure of grapheneformed on the silicon suboxide or on the porous silicon secondarycomposite particle.

In an embodiment, the silicon-containing composite may further include ametal oxide or a metal fluoride. When the silicon-containing compositefurther includes a metal oxide or a metal fluoride, formation of an SEIlayer may be prevented due to suppression of a side reaction.

The metal oxide may include a magnesium oxide, a manganese oxide, analuminum oxide, a titanium oxide, a zirconium oxide, a tantalum oxide, atin oxide, a hafnium oxide, or a combination thereof. The metal fluoridemay include an aluminum fluoride (AlF₃). A combination comprising atleast one of the foregoing may also be used.

In an embodiment, graphene in the silicon-containing composite may serveas an SEI stabilization clamping layer. The silicon-containing compositemay have a large specific surface area, and thus may prevent a reductionin initial efficiency and volume energy density of a battery when usedin the battery.

The graphene in the silicon-containing composite may suppressdisintegration or pulverization of active materials such as silicon, andmay improve conductivity of the silicon-containing composite. Thegraphene may suppress disintegration or pulverization of siliconparticles. The graphene may serve as a clamping layer which preventsdisintegration of silicon particles, while also allowing for an alloyingreaction between lithium ions and silicon (Si) to thereby yield asignificant specific capacity and provide a continuous conductionpathway between the particles.

The graphene layers may slide over each other when the silicon particlesswell during charging, and then slide back to their relaxed positionsduring delithiation. Without being limited by theory, it is understoodthat this movement occurs because the van der Waals force is greaterthan the force of friction between the layers.

The clamping effect of the graphene layers, which preventsdisintegration of silicon particles and allows the graphene layers toserve as a clamping layer, may be confirmed by evaluating whether thegraphene layers remain the same (are unaffected) after about 200repeated lithiation/delithiation cycles.

In an embodiment, the silicon-containing composite may include nanosizedpores between closely compacted graphene on the silicon compositeprimary particles, the pores serving as a buffer during the volumeexpansion of the primary and secondary particles. An SEI layer may alsobe stably grown on the primary particles through thermal treatment. Thegraphene layers on the secondary particles may slide over one another,expanding their volume while the volume expansion and contraction ofsilicon occurs, to thereby prevent the primary particles from beingexposed to the environment outside of the secondary particles, and thussuppress contact between the silicon composite primary particles and anelectrolyte.

According to another aspect, a carbon composite includes asilicon-containing composite according to any of the above-describedembodiments and a carbonaceous material. A silicon-containing compositeaccording to any of the embodiments may have a reduced specific surfacearea and an increased volume density (specific capacity), as comparedwith silicon composite primary particles, and thus may improve volumeenergy density and further reduce volume expansion of an electrode whenmixed with a carbonaceous material.

The carbon composite may further improve initial efficiency, specificcapacity characteristics, rate capability, and durability, as comparedto when the silicon-containing composite is used alone (without thecarbonaceous material coating).

In an embodiment, an amount of the carbonaceous material may be about0.001 parts to about 99 parts by weight, and in another embodiment,about 10 parts to about 97 parts by weight, and in another embodiment,about 50 parts to about 97 parts by weight, based on 100 parts by weightof the carbon composite.

The carbonaceous material may include graphene, graphite, a fullerene, acarbon fiber, a carbon nanotube, or a combination thereof.

In an embodiment, the carbon composite may include, for example,graphite and the silicon-containing composite formed on the graphite.

The graphite may be, for example, SFG₆ graphite (TIMREX®), and may havean average particle diameter of about 6 μm. When an electrode is formedusing the carbon composite, an amount of the carbon composite in theelectrode may be, for example, about 65 parts to 100 parts by weight, orabout 65 parts to about 90 parts by weight, or from about 68 parts toabout 87 parts by weight, and an amount of a binder may be, for example,about 10 parts by weight to about 50 parts by weight, or about 12 partsto about 40 parts by weight, or from about 13 parts to about 32 parts byweight. For example, an amount of the graphite in the carbon compositemay be, for example, about 0.5 part to about 30 parts by weight, orabout 1 part to about 25 parts by weight, or 1 part to about 20 parts byweight based on 100 parts by weight of the carbon composite.

The binder may be, for example, lithium polyacrylate.

The compound represented by Formula 1 and the compound represented byFormula 2 may each independently be methane, ethylene, propylene,methanol, ethanol, propanol, or a combination thereof.

The oxygen-containing compound represented by Formula 3 may include, forexample, carbon dioxide (CO₂), carbon monoxide (CO), water vapor (H₂O),or a combination thereof.

The N precursor may be, for example, ammonia.

Examples of the S precursor may include sulfur powder, (NH₄)₂SO₄,Li₂SO₄, CoSO₄, or a combination thereof. Examples of the P precursor mayinclude phosphorous powder, (NH₄)₂HPO₄, NH₄H₂PO₄, Li₃PO₄, P₂O₅, or acombination thereof.

In an embodiment, at least one inert gas selected from the groupconsisting of nitrogen, helium, and argon may be further added to, thecarbon source gas.

The oxygen-containing gas may include carbon monoxide, carbon dioxide,water vapor, or a combination thereof.

When the oxygen-containing gas is used as the carbon source gas, thesilicon suboxide may be formed to have an increased thickness ascompared with a thickness of a naturally-occurring silicon suboxidelayer. For example, a thickness of the silicon suboxide may be about 10nm or less, or about 5 nm or less, or about 1 nm or less, for example,from about 0.1 to about 10 nm, or from about 0.5 nm to about 7.5 nm, orfrom about 0.5 nm to about 5 nm. When the thickness of the siliconsuboxide is within these ranges, a shape and a thickness of the graphenemay be appropriately controlled. In particular, when the siliconsuboxide has a thickness greater than that of a naturally-occurringsilicon suboxide layer, the graphene layer on the silicon suboxide mayhave a denser structure than a graphene nanosheet. The graphene layermay include, for example, 5 to 10 graphene layers.

When the gas mixture includes water vapor, the conductivity of thecomposite may further be improved. While not being limited by theory, itis understood that since carbon having a high degree of crystallinitymay be deposited, in the presence of water vapor, on the silicon coatedwith the silicon suboxide by reaction with the gas mixture, the carboncomposite may have high conductivity even when coated with a smallamount of carbon. The amount of water vapor in the gas mixture, thoughnot specifically limited, may be, for example, in a range of about 0.01%by volume to about 10% by volume, or about 0.05% to about 7.5% byvolume, or about 0.1 to about 5% by volume based on 100% by volume ofthe carbon source gas.

In an embodiment, the carbon source gas may include methane, a mixed gasof methane and an inert gas, an oxygen-containing gas, or a mixed gas ofmethane and an oxygen-containing gas.

In another embodiment, the carbon source gas may be a mixed gas of CH₄and CO₂, or a mixed gas of CH₄, CO₂, and H₂O. In another embodiment, themorphology of the graphene may be varied depending on a type of thecarbon source in the gas.

The mixed gas of CH₄ and CO₂ may be supplied at a molar ratio of about1:0.20 to about 1:0.50, and in an embodiment, at a molar ratio of about1:0.25 to about 1:0.45, and in another embodiment, at a molar ratio ofabout 1:0.30 to about 1:0.40.

The mixed gas of CH₄, CO₂, and H₂O may be supplied at a molar ratio ofabout 1:0.20:1 to 0.50:0.01 to 1.45, and in an embodiment, at a molarratio of about 1:0.25:1 to 0.45:0.10 to 1.35, and in another embodiment,at a molar ratio of about 1:0.30:1 to 0.40:0.50 to 1.0.

In an embodiment, the carbon source gas may be carbon monoxide (CO) orcarbon dioxide (CO₂).

In another embodiment, the carbon source gas may be a mixed gas of CH₄and N₂.

The mixed gas of CH₄ and N₂ may be supplied at a molar ratio of about1:0.20 to about 1:0.50, and in an embodiment, at a molar ratio of about1:0.25 to 1:0.45, and in another embodiment, at a molar ratio of about1:0.30 to about 1:0.40. In another embodiment, the carbon source gas maynot include an inert gas such as nitrogen.

The thermal treatment may be performed at a temperature of about 750° C.to about 1,100° C., and in some embodiments, about 800° C. to about1,000° C.

The thermal treatment may be performed at any pressure level withoutlimitation. The pressure level for the thermal treatment may beappropriately selected in consideration of a thermal treatmenttemperature, composition of the gas mixture, and target amount of coatedcarbon. The pressure level for the thermal treatment may be controlledby varying the amounts of inflow and outflow of the gas mixture. Forexample, the pressure for the thermal treatment may be about 1atmosphere (atm) or greater, and in some embodiments, about 2 atm orgreater, about 3 atm or greater, about 4 atm or greater, or about 5 atmor greater. However, embodiments are not limited thereto.

The thermal treatment time may not be specifically limited, and may beappropriately controlled depending on the thermal treatment temperature,thermal treatment pressure, composition of the gas mixture, and targetamount of coated carbon. For example, the thermal treatment time may bein a range of about 10 minutes to about 100 hours, and in an embodiment,may be in a range of about 30 minutes to about 90 hours, and in anotherembodiment, may be in a range of about 50 minutes to about 40 hours.However, embodiments are not limited thereto. While not limited to thistheory, it is understood that the longer the thermal treatment time, thegreater the amount of graphene (carbon) that may be deposited, and thebetter the electrical characteristics of the composite may become.However, these effects may not be directly proportional to the thermaltreatment time. For example, deposition of graphene may stop or thedeposition rate may become low after a predetermined duration.

According to an embodiment, a method of preparing a silicon-containingcomposite according to any one of the embodiments may provide a uniformcoating of graphene on the silicon covered with the silicon suboxide(SiO_(x)), even at a relatively low temperature, through a vapor phasereaction of the carbon source gas as described above. Separation of thegraphene from the silicon covered with the silicon suboxide (SiO_(x))may substantially not occur. When the thickness of the silicon suboxideis appropriately controlled, the separation of the graphene may be evenfurther suppressed. In this regard, a thickness of the silicon suboxidethat may efficiently suppress separation of the graphene is about 10 nmor less, or about 7.5 nm or less, or about 5 nm or less, or about 2 nmor less, for example, from about 0.1 nm to about 10 nm, or about 0.1 nmto about 7.5 nm, or for example, from about 0.1 nm to about 5 nm.

Since the graphene is coated on the silicon suboxide through a vaporphase reaction to form a coating layer, the coating layer may have ahigh degree of crystallinity. When the porous silicon-containingcomposite is used as a negative active material, the negative activematerial may have improved conductivity without a structural change.

In an embodiment, the vapor deposition reaction for preparing asilicon-containing composite according to one or more embodiments may beperformed in an atmosphere of a gas mixture including a carbon mixed gasand a reducing gas, such as hydrogen.

In an embodiment, when the silicon composite primary particles in asilicon-containing composite according to one or more embodimentsinclude a silicon suboxide of the Formula SiO_(x), wherein 0<x<2 athermal treatment product of a silicon suboxide of the Formula SiOx,wherein 0<x<2, or a combination thereof; and a first graphene disposedon the silicon suboxide, the thermal treatment product of the siliconsuboxide, or the combination thereof, the first graphene may be obtainedby thermal treatment, for example, in an atmosphere including a gasmixture including a carbon source gas, such as methane, and hydrogen.For example, a mixed ratio of the carbon source gas to hydrogen may beabout 1:1 to about 1:7, an in an embodiment, about 1:1 to about 1:5, orabout 1:1 to about 1:3, by mole or by flow rate.

A process of preparing a carbon composite using a silicon-containingcomposite according to any of the embodiments may be as follows.

A silicon-containing composite according to an embodiment and acarbonaceous material may be mixed together and thermally treated.

The thermal treatment may be performed at a temperature of about 600° C.to about 1,100° C., for example about 700° C. to about 1,000° C. Whenthe thermal treatment temperature is within these ranges, a carboncomposite with improved capacity characteristics may be attained.

In the silicon-containing composite according to one or moreembodiments, a carbon (C) to silicon (Si) atomic ratio (hereinafter,referred to as C/Si atomic ratio) obtained by X-ray photoelectronspectrometry (XPS) analysis may be from about 100:1 to about 200:1, forexample, about 140:1 to about 180:1. In an embodiment, the C/Si atomicratio in the silicon-containing composite obtained by XPS analysis maybe increased as compared with that in a silicon-containing composite notincluding the at least one element selected from N, P, and S. Here, suchan increase may be increased by, for example, 300% or more, and forexample, 490% or more. The increase in the C/Si atomic ratio may referto an increase in a covering ratio of the graphene on the surface of thesilicon/silicon oxide.

In an embodiment, a silicon-containing composite or a carbon compositeaccording to any of the above-described embodiments may be used in, forexample, a battery, a light emission material for a display, a fieldemission material for a display, a thermoelectric device, or abiosensor.

According to another aspect, an electrode includes a silicon-containingcomposite or a carbon composite according to any of the above-describedembodiments.

The electrode may be an electrode for a lithium battery.

The electrode may be a negative electrode.

The silicon-containing composite or the carbon composite may be used asan electrode active material, for example, a negative active material.In this regard, when the silicon-containing composite or the carboncomposite is used as a negative active material, volume expansion anddisintegration of silicon may be reduced or prevented.

The negative active material may have improved conductivity, and mayimprove high-rate characteristics of, for example, a lithium ionbattery. Moreover, since a small amount of graphene may be coated on thesilicon covered with the silicon suboxide, the negative active materialmay have improved energy density per volume. A lithium ion battery maybe provided which may include the silicon-containing composite or thecarbon composite, the carbon composite including a silicon-containingcomposite according to any of the embodiments and a carbonaceousmaterial.

In an embodiment, the negative electrode may be manufactured in thefollowing manner.

The negative electrode may be formed by molding, into a predeterminedshape, a negative active material composition which may include, forexample, a silicon-containing composite or a carbon composite accordingto an embodiment as a negative active material, a conducting agent, anda binder. Alternatively, the negative electrode may be formed by coatingthe negative active material composition on a current collector, such asa copper (Cu) foil. Also, the negative active material composition maynot include a conducting agent.

In an embodiment, the negative active material composition may be formedas a film on a separator without the current collector.

In particular, the negative active material composition may be preparedby mixing the negative active material, a conducting agent, a binder,and a solvent. The negative active material composition may be directlycoated on a metal current collector to form a negative electrode plate.In some embodiments, the negative active material composition may becast onto a separate support to form a negative active material film.

The negative active material film may be separated from the support andthen laminated on a metal current collector to thereby form a negativeelectrode. The negative electrode is not limited to having theabove-listed forms, and may have any of a variety of forms.

The negative active material composition may further include acarbonaceous negative active material, in addition to theabove-described negative active material. For example, the carbonaceousnegative active material may include natural graphite, artificialgraphite, expansion graphite, graphene, carbon black, fullerene soot,carbon nanotubes, carbon fibers, or a combination thereof. However,embodiments are not limited thereto. Any suitable carbonaceous negativeactive material may be used.

The conducting agent may be acetylene black, ketjen black, naturalgraphite, artificial graphite, carbon black, carbon fibers, a metalpowder or metal fibers of copper, nickel, aluminum, or silver, or acombination thereof. The conducting agent may include one or moreconductive materials, such as a polyphenylene derivative, incombination.

However, embodiments are not limited thereto. Any suitable conductingagent may be used.

The binder may be a vinylidene fluoride/hexafluoropropylene copolymer,polyvinylidenefluoride (PVDF), polyacrylonitrile,polymethylmethacrylate, polytetrafluoroethylene, a styrene-butadienerubber-based polymer, polyacrylic acid, polyamide imide, polyimide, or acombination thereof. However, embodiments are not limited thereto. Anysuitable binder may be used.

The solvent may be N-methylpyrrolidone, acetone, water, or a combinationthereof. However, embodiments are not limited thereto. Any suitablesolvent available in the art may be used.

Amounts of the negative active material, the conducting agent, thebinder, and the solvent may be may be determined by those of skill inthe art without undue experimentation. At least one of the conductingagent, the binder, and the solvent may be omitted depending on the useand structure of a lithium battery.

In an embodiment, a lithium battery may include the negative electrode.The lithium battery may be manufactured in the following manner.

First, a negative electrode may be manufactured according to theabove-described method of manufacturing a negative electrode.

Next, a positive active material composition may be prepared by mixing apositive active material, a conducting agent, a binder, and a solvent.The positive active material composition may be directly coated on ametal current collector and dried to manufacture a positive electrode.In some other embodiments, the positive active material composition maybe cast on a separate support to form a positive active material layer.The positive active material layer may then be separated from thesupport and then laminated on a metal current collector, to therebymanufacture a positive electrode.

The positive active material may include lithium cobalt oxide, lithiumnickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide,lithium iron phosphorous oxide, lithium manganese oxide, or acombination thereof. However, embodiments are not limited thereto. Anysuitable positive active material may be used.

For example, the positive active material may be a lithium-containingmetal oxide.

Any suitable positive active material may be used. For example, thepositive active material may include a composite lithium oxide includingcobalt (Co), manganese (Mn), nickel (Ni), or a combination thereof. Forexample, the positive active material may be a compound represented bythe following formulae: Li_(a)A_(1−b)B_(b)D₂ (wherein 0.90≤a≤1 and0≤b≤0.5); Li_(a)E_(1−b)B_(b)O_(2−c)D_(c) (wherein 0.90≤a≤1, 0≤b≤0.5, and0≤c≤0.05); LiE_(2−b)B_(b)O_(4−c)D_(c) (wherein 0≤b≤0.5 and 0≤c≤0.05)Li_(a)Ni_(1−b−c)CO_(b)B_(c)D_(α) (wherein 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05,and 0≤α≤2) Li_(a)Ni_(1−b−c)Co_(b)B_(c)O_(2−α)F_(α) (wherein 0.90≤a≤1,0≤b≤0.5, 0≤c≤0.05, and 0<α<2) Li_(a)Ni_(1−b−c)Co_(b)B_(c)O_(2−α)F₂(wherein 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2)Li_(a)Ni_(1−b−c)Mn_(b)B_(c)D_(a) (wherein 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05,and 0<α≤2) Li_(a)Ni_(1−b−c)Mn_(b)B_(c)O_(2−a)F_(α) (wherein 0.90≤a≤1,0≤b≤0.5, 0≤c≤0.05, and 0<α<2) Li_(a)Ni_(1−b−c)Mn_(b)B_(c)O_(2−α)F₂(wherein 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0≤α<2)Li_(a)Ni_(b)E_(c)G_(d)O₂ (wherein 0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, and0.001≤d≤0.1); Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂ (wherein 0.90≤a≤1, 0≤b≤0.9,0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1); Li_(a)NiG_(b)O₂ (wherein 0.90≤a≤1and 0.001≤b≤0.1); Li_(a)CoG_(b)O₂ (wherein 0.90≤a≤1 and 0.001≤b≤0.1);Li_(a)MnG_(b)O₂ (wherein 0.90≤a≤1 and 0.001≤b≤0.1); Li_(a)Mn₂GbO₄(wherein 0.90≤a≤1 and 0.001≤b≤0.1); QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₅;LiIO₂; LiNiVO₄; Li_((3-f))J₂(PO₄)₃ (0≤f≤2); Li_((3-f))Fe₂(PO₄)₃ (0≤f≤2);and LiFePO₄.

In the formulae above, A may be nickel (Ni), cobalt (Co), manganese(Mn), or a combination including at least one of the foregoing; B may bealuminum (Al), nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr),iron (Fe), magnesium (Mg), strontium (Sr), vanadium (V), a rare earthelement, or a combination including at least one of the foregoing; D maybe oxygen (O), fluorine (F), sulfur (S), phosphorus (P), or acombination including at least one of the foregoing; E may be cobalt(Co), manganese (Mn), or a combination including at least one of theforegoing; F may be fluorine (F), sulfur (S), phosphorus (P), or acombination including at least one of the foregoing; G may be aluminum(Al), chromium (Cr), manganese (Mn), iron (Fe), magnesium (Mg),lanthanum (La), cerium (Ce), strontium (Sr), vanadium (V), or acombination including at least one of the foregoing; Q may be titanium(Ti), molybdenum (Mo), manganese (Mn), or a combination including atleast one of the foregoing; may be chromium (Cr), vanadium (V), iron(Fe), scandium (Sc), yttrium (Y), or a combination including at leastone of the foregoing; and J may be vanadium (V), chromium (Cr),manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), or a combinationincluding at least one of the foregoing.

The compounds listed above as positive active materials may have asurface coating layer (hereinafter, “coating layer”). Alternatively, amixture of a compound without a coating layer and a compound having acoating layer, the compounds being the compounds listed above, may beused. The coating layer may include an oxide, hydroxide, oxyhydroxide,oxycarbonate, hydroxycarbonate, or a combination including at least oneof the foregoing. The compounds for the coating layer may be amorphousor crystalline. The coating element for the coating layer may bemagnesium (Mg), aluminum (Al), cobalt (Co), potassium (K), sodium (Na),calcium (Ca), silicon (Si), titanium (Ti), vanadium (V), tin (Sn),germanium (Ge), gallium (Ga), boron (B), arsenic (As), zirconium (Zr),or a combination including at least one of the foregoing. The coatinglayer may be formed by any suitable method that does not substantiallyadversely affect the physical properties of the positive active materialwhen a compound of the coating element is used, for example, by a spraycoating method, a dipping method, or the like. These methods are isknown in the art, and thus a detailed description thereof will beomitted.

For example, the positive active material may be LiNiO₂, LiCoO₂,LiMn_(x)O_(2x) (wherein x may be 1 or 2), LiNi_(1−x)Mn_(x)O₂ (wherein0<x<1), LiNi_(1−x−y)Co_(x)Mn_(y)O₂ (wherein 0≤x≤0.5 and 0≤y≤0.5),LiFeO₂, V₂O₅, TiS, MoS, or a combination including at least one of theforegoing.

The conducting agent, the binder, and the solvent used in the positiveactive material composition may be the same as those used in thenegative active material composition described above. In an embodiment,a plasticizer may further be included in the positive active materialcomposition and/or the negative active material composition to obtain anelectrode plate including pores.

Amounts of the positive active material, the conducting agent, thebinder, and the solvent may be the same as those suitably used inlithium batteries. At least one of the conducting agent, the binder, andthe solvent may be omitted depending on the use and structure of alithium battery.

Next, a separator to be disposed between the positive electrode and thenegative electrode may be prepared. The separator may be any suitableseparator material used in lithium batteries. In an embodiment, theseparator material may have a low resistance to migration of ions in anelectrolyte and have a good electrolyte-retaining ability. For example,the separator material may be glass fiber, polyester, Teflon,polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or acombination including at least one of the foregoing, each of which maybe a non-woven or woven fabric. For example, a rollable separatorincluding polyethylene or polypropylene may be used in a lithium ionbattery. A separator or separator material with a suitable organicelectrolytic solution-retaining ability may be used in a lithium ionpolymer battery. For example, the separator may be manufactured in thefollowing manner.

In an embodiment, a polymer resin, a filler, and a solvent may becombined, for example by mixing, to prepare a separator composition.Then, the separator composition may be directly coated on a support andthen dried to thereby form the separator. In another embodiment, theseparator composition may be cast on a support and dried to form aseparator film. The separator film may be separated from the support andlaminated on an electrode to thereby form the separator.

The polymer resin used to manufacture the separator may be any suitablematerial used as a binder for electrode plates. For example, the polymerresin may be a vinylidene fluoride/hexafluoropropylene copolymer, PVDF,polyacrylonitrile, poly(methyl(meth)acrylate), or a combinationincluding at least one of the foregoing.

The separator may include a ceramic composition to improve the separatorfunctioning as a membrane. For example, the separator may be coated withan oxide or may be formed to include ceramic particles.

Next, an electrolyte may be prepared.

For example, the electrolyte may be an organic electrolyte. Theelectrolyte may be solid. For example, the electrolyte may be a boronoxide, a lithium oxynitride, or a combination including at least one ofthe foregoing. However, embodiments are not limited thereto. Anysuitable solid electrolyte may be used. The solid electrolyte may beformed on the negative electrode by a suitable method, for example, bysputtering.

For example, an organic electrolyte may be prepared. The organicelectrolyte may be prepared by dissolving a lithium salt in an organicsolvent.

The organic solvent may be any suitable organic solvent. For example,the organic solvent may be propylene carbonate, ethylene carbonate,fluoroethylene carbonate, butylene carbonate, dimethyl carbonate,diethyl carbonate, methylethyl carbonate, methylpropyl carbonate,ethylpropyl carbonate, methylisopropyl carbonate, dipropyl carbonate,dibutyl carbonate, chloroethylene carbonate, benzonitrile, acetonitrile,tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane,4-methyldioxolane, N,N-dimethyl formamide, N,N-dimethyl acetamide,N,N-dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane,dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethylether, or a combination including at least one of the foregoing.

The lithium salt may be any suitable lithium salt. For example, thelithium salt may be LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiCF₃SO₃,Li(CF₃SO₂)₂N, Li(FSO₂)₂N, LiC₄F₉SO₃, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein x and y may be naturalnumbers), LiCl, LiI, or a combination including at least one of theforegoing.

Referring to FIG. 12A, a lithium battery 121 according to an embodimentmay include a positive electrode 123, a negative electrode 122, and aseparator 124. The positive electrode 123, the negative electrode 122,and the separator 124 may be wound or folded, and then sealed in abattery case 125. Then, the battery case 125 may be filled with anorganic liquid electrolyte and sealed with a cap assembly 126, therebycompleting the manufacture of the lithium battery 121. The battery case125 may be a cylindrical type, a rectangular type, or a thin-film type.For example, the lithium battery 121 may be a thin-film type battery.For example, the lithium battery 121 may be a lithium ion battery.

The separator 124 may be interposed between the positive electrode 123and the negative electrode 122 to form a battery assembly. A pluralityof such battery assemblies may be stacked in a bi-cell structure andimpregnated with an organic electrolyte solution. The resultant batteryassembly may then be put into a pouch and hermetically sealed to therebycomplete the manufacture of a lithium ion battery.

In an embodiment, a plurality of battery assemblies may be stacked uponone another to form a battery pack, which may be used in any device thatbenefits from high capacity and high output, for example, in a laptopcomputer, a smartphone, an electric vehicle, or the like.

The lithium battery including such a battery pack may have improvedhigh-rate characteristics and lifetime characteristics, and thus may beapplicable in an electric vehicle (EV), for example, in a hybrid vehiclesuch as plug-in hybrid electric vehicle (PHEV).

According to another aspect, a field emission device includes asilicon-containing composite or a carbon composite according to any oneof the embodiments.

The field emission device is a device which is based upon the migrationof electrons. The field emission device may include, at least, areduction electrode, an emitter tip, and an oxidation electrodeseparated from the reduction electrode. Examples of such a fieldemission device are disclosed in U.S. Pat. Nos. 7,009,331; 6,976,897;6,911,767; and US 2006/0066217, the disclosures of which areincorporated in their entirety by reference. The emitter tip may emitelectrons as a voltage is applied between the reduction electrode andthe oxidation electrode. The electrons may migrate from the reductionelectrode toward the oxidation electrode. A field emission deviceaccording to an embodiment of the present disclosure may be used forvarious purposes, for example, in ultrasonic vacuum tube equipment (forexample, an X-ray tube), a power amplifier, an ion gun, a high-energyaccelerator, a free-electron laser, or an electron microscope, and in anembodiment, in a flat display device. A flat display device may be usedas an alternative to a cathode tube, and may also be applicable in a TVor a computer monitor.

The silicon-containing composite or a carbon composite according to anyone of the embodiments may be used as the emitter tip.

The emitter tip may be manufactured using a metal such as molybdenum(Mo) or a semiconductor such as silicon. One of the concerns with usingthe metal emitter is a comparatively high control voltage of about 100volts (V) for emission. In addition, due to non-uniformity of suchemitter tips, current densities of individual pixels of a field emissiondevice using the emitter tips may be non-uniform.

When a silicon-containing composite or a carbon composite according toany one of the embodiments is used as the emitter tip, the fieldemission device may have improved field emission characteristics.

The silicon-containing composite or carbon composite according to anyone of the embodiments may be used to manufacture an electroluminescentdevice.

According to another aspect, a biosensor includes a silicon-containingcomposite or a carbon composite according to any one of theabove-described embodiments.

The silicon-containing composite or the carbon composite according toany one of the embodiments may be used to form an electrode for abiosensor.

FIG. 12E is a cross-sectional view illustrating a structure of anelectrode of a biosensor according to an embodiment of the presentdisclosure.

Referring to FIG. 12E, the electrode of a biosensor may include asubstrate 310, a first layer 320 on the substrate 310, the first layer320 including a porous silicon-containing' composite or carbon compositeaccording to any one of the embodiments, and a second layer 330 on thefirst layer 320. A biomaterial 340 may be supported by or fixed in thesecond layer 330 in a variety of manners.

The substrate 310 may be any suitable plate on which graphene may bedeposited or formed, and for example, may be glass, plastic, metal,ceramic, silicon, or a combination including at least one of theforegoing. The type of the substrate 310 is not specifically limited,provided that graphene may be deposited or formed thereon.

The biomaterial 340 may be enzymes, aptamers, proteins, nucleic acids,microorganisms, cells, lipids, hormones, DNA, PNA, RNA, or a combinationincluding at least one of the foregoing. Any of various suitablebiomaterials, not already stated herein, may also be used.

Referring to FIG. 12E, in the electrode of a biosensor, the biomaterial340 may be an enzyme, and the second layer 330 may be a layer able tosupport or fix the enzyme therein. Although according to FIG. 12E anenzyme as the biomaterial 340 appears as being supported or fixed in thesecond layer 330, the location of the enzyme is not limited thereto, andthe enzyme may partially or entirely protrude through the surface of thesecond layer 330 and be exposed (not shown). When a biosensor has thisstructure including an enzyme with substrate specificity to selectivelyrespond to a target molecule in a mixture, the biosensor may selectivelysense an analyte (for example, blood sugar) to which the enzymeresponds.

According to another aspect, a semiconductor device includes asilicon-containing composite or a carbon composite according to any oneof the above-described embodiments.

The silicon-containing composite or the carbon composite may be used asan electrode of the semiconductor device.

According to another aspect, there are provided a thermoelectricmaterial and a thermoelectric device, each including asilicon-containing composite or a carbon composite according to any oneof the above-described embodiments.

The thermoelectric material may have good electrical characteristics,and consequently may have improved thermoelectric performance. Thethermoelectric material may be used in a thermoelectric device, athermoelectric module, or a thermoelectric system.

The performance of the thermoelectric material is evaluated using adimensionless figure of merit (ZT), which is defined by Equation 1:ZT=(S ² σT)/k  [Equation 1]

wherein, in Equation 1, ZT is a figure of merit, S is a Seebeckcoefficient, σ is an electrical conductivity, T is an absolutetemperature, and K is a thermal conductivity.

As represented in Equation 1, an increase in the ZT value of athermoelectric material may be obtained by increasing the Seebeckcoefficient (S) and the electrical conductivity (σ) of thethermoelectric material, i.e., a power factor (S²σ), and reducing thethermal conductivity (k) of the thermoelectric material.

The silicon-containing composite or carbon composite according to anyone of the above-described embodiments includes graphene, and thus mayprovide high electrical conductivity and low thermal conductivity to athermoelectric material when included therein, according to thecharacteristics of the graphene, and thus improve the performance of thethermoelectric material.

In a silicon-containing composite or carbon composite according to anyone of the above-described embodiments, crystalline characteristics andan electron structure may be changed at an interface between themetallic graphene and semi-conductive silicon to increase a Seebeckcoefficient thereof and accelerate transfer of charge particles, whichmay consequently induce an increase in electrical conductivity andcharge mobility. In addition, phonon scattering at the interface betweenthe graphene and silicon may be increased so that it may be possible tocontrol the thermal conductivity of the thermoelectric material.

The silicon-containing composite or the carbon composite according toany one of the above-described embodiments may be effectively used as athermoelectric material. A thermoelectric device may be manufactured byprocessing the thermoelectric material into a shape, for example, bycutting. The thermoelectric device may be a p-type thermoelectricdevice. The thermoelectric device may be a structure formed by shapingthe thermoelectric material in a predetermined shape, for example, in arectangular parallelepiped shape.

The thermoelectric device may have a cooling effect when combined withan electrode and a current is applied thereto, and may have a powergeneration effect based on a temperature difference.

FIG. 12B is a schematic view of a thermoelectric module 200 using athermoelectric device according to an embodiment of the presentdisclosure. Referring to FIG. 12B, an upper electrode (first electrode)212 and a lower electrode (second electrode) 222 are patterned on anupper insulating substrate 211 and a lower insulating substrate 221,respectively. The upper electrode 212 and the lower electrode 222 maycontact a p-type thermoelectric component 215 and an n-typethermoelectric component 216. The upper electrode 212 and the lowerelectrode 222 may be connected to the outside of the thermoelectricdevice by a lead electrode 224. The p-type thermoelectric component 215may be a thermoelectric device according to any one of theabove-described embodiments. The n-type thermoelectric component 216 maynot be specifically limited, and may be any suitable material known inthe art.

The upper and lower insulating substrates 211 and 221 may includegallium arsenide (GaAs), sapphire, silicon, Pyrex, quartz, or acombination including at least one of the foregoing. The upper and lowerelectrodes 212 and 222 may include, for example, copper, aluminum,nickel, gold, titanium, or a combination including at least one of theforegoing, and may have various sizes. The upper and lower electrodes212 and 222 may be formed using any suitable patterning method, forexample, a lift-off semiconductor process, a deposition method, aphotolithography technique, or a combination including at least one ofthe foregoing.

In an embodiment, one of the first and second electrodes 212 and 222 inthe thermoelectric module may be exposed to a heat source as illustratedin FIGS. 12C and 2D. In some other embodiments, one of the first andsecond electrodes 212 and 222 in the thermoelectric module may beelectrically connected to a power supply source, or to the outside ofthe thermoelectric module, for example, an electric device (for example,a battery) that consumes or stores electric power.

In an embodiment, one of the first and second electrodes 212 and 222 inthe thermoelectric module may be electrically connected to a powersupply source.

One or more embodiments of the present invention will now be describedin detail with reference to the following examples. However, theseexamples are only for illustrative purposes and are not intended tolimit the scope of the one or more embodiments of the present invention.

EXAMPLES Preparation Example 1

Needle-like silicon was pulverized to obtain plate-like and needle-likesilicon particles having a silicon suboxide (SiO_(x), wherein 0<x<2)film (having a thickness of about 0.1 nm) on a surface thereof andhaving a particle length (D90) of about 150 nm and a thickness of about40 nm.

A composition including 25 parts by weight of the plate-like andneedle-like silicon particles, 10 parts by weight of stearic acid, and65 parts by weight of isopropyl alcohol was spray-dried, and then driedto obtain porous silicon composite secondary particles having an averageparticle diameter in a range of about 3 μm to about 6 μm.

The spray-drying was performed using a spray drier (MMSD Micro MistSpray Dryers, Fujisaki Electric). The spray nozzle size, pressure undera N₂ atmosphere, and powder spray temperature (about 200° C.) werecontrolled, and then the resultant was dried to prepare porous siliconcomposite secondary particles from which isopropyl alcohols wereremoved. The spray nozzle size was controlled to about 150 μm, and thespray nozzle was about 0.6 MPa.

The porous silicon composite secondary particles were loaded into areactor. A N₂ gas was purged into the reactor, and as a reaction gas, agas mixture was supplied into the reactor to create an atmosphere of thegas, the gas mixture containing a composition shown in Table 1. Here,the pressure level inside the reactor resulting from the supply of thegas was 1 atm. The internal temperature of the reactor was increased to1,000° C. (at a rate of about 23° C./min) under the atmosphere of thegas. While the gas was continuously supplied into the reactor, thermaltreatment was performed at 1,000° C. for about 1 hour. The resultingproduct was left for about 3 hours. Afterwards, the supply of the gaswas stopped, and the reactor was cooled down to room temperature (25°C.), and nitrogen a N₂ gas was purged into the reactor again, therebyobtaining a silicon-containing composite. The silicon-containingcomposite is porous.

A total amount of a first graphene and a second graphene in thesilicon-containing composite was about 25 parts by weight, based on 100parts by weight of a total weight of the silicon-containing composite.

Preparation Example 2-6

Silicon-containing composite were obtained in the same manner as inPreparation Example 1, except that, as the reaction gas, a gas mixtureincluding a composition of Table 1 was each used.

Preparation Example 7

A silicon-containing composite was obtained in the same manner as inPreparation Example 1, except that, as the plate-like and needle-likesilicon particles, plate-like and needle-like silicon particles having asilicon suboxide (SiO_(x), wherein 0<x<2) film (having a thickness ofabout 0.1 nm) on a surface thereof and having a length (D90) of about200 nm and a thickness of about 40 nm were used.

Preparation Example 8

A silicon-containing composite was obtained in the same manner as inPreparation Example 1, except that, as the plate-like and needle-likesilicon particles, plate-like and needle-like silicon particles having asilicon suboxide (SiO_(x), wherein 0<x<2) film (having a thickness ofabout 0.1 nm) on a surface thereof and having a length (D90) of about100 nm and a thickness of about 40 nm were used.

Reference Preparation Example 1

A silicon-containing composite was obtained in the same manner as inPreparation Example 1, except that as the plate-like and needle-likesilicon particles, plate-like and needle-like silicon particles having asilicon suboxide (SiO_(x), wherein 0<x<2) film (having a thickness ofabout 0.1 nm) on a surface thereof and having a length (D90) of about200 nm and a thickness of about 40 nm were used, and that, as thereaction gas, a gas mixture including a composition of Table 1 was used.

As shown in Table 1, the first graphene and the second graphene includedin the each of the porous silicon-containing composites preparedaccording to Preparation Examples 1 to 8 were in the form of either afilm or a flake. The first graphene and the second graphene were foundto usually have a film form in a region adjacent to the siliconsuboxide, and a flake form in a region away from the adjacent region.The first graphene and the second graphene included in the poroussilicon-containing composite prepared according to Preparation Example 5were more likely to be present in the form of a film, as compared withthose included in the porous silicon-containing composites preparedaccording to Preparation Examples 1 to 4 and Preparation Example 6 to 8.

TABLE 1 Size of silicon particles (length of long axis of plate- andneedle-like Reaction gas Form of first silicon particle) (volume %)graphene and (nm) CH₄ CO₂ NH₃ second graphene Preparation 150 80 10 10Film + flake Example 1 Preparation 150 95 — 5 Film + flake Example 2Preparation 150 90 — 10 Film + flake Example 3 Preparation 150 80 — 20Film + flake Example 4 Preparation 150 60 20 20 Film + flake Example 5Preparation 150 90 5 5 Film + flake Example 6 Preparation 200 80 10 10Film + flake Example 7 Preparation 100 80 10 10 Film + flake Example 8Reference 200 100 0 0 Film Preparation Example 1

Comparative Preparation Example 1

A composition including 20 parts by weight of granule-like siliconhaving a size of 10 μm, 10 parts by weight of stearic acid, and 70 partsby weight of isopropyl alcohol was pulverized to prepare a slurryincluding needle-like silicon particles. The slurry was dried without aspraying process.

The resulting product was pulverized to obtain needle-like siliconparticles having a length of 125 nm having a silicon suboxide (SiO_(x),wherein 0<x<2) film (having a thickness of about 0.1 nm).

The needle-like silicon particles were loaded into a reactor. A N₂ gas(300 sccm) was supplied into the reactor to create an atmosphere of thegas. Here, the pressure level inside the reactor resulting from thesupply of the gas was 1 atm. The internal temperature of the reactor wasincreased to 950° C. (at a rate of about 23° C./min) under theatmosphere of the gas. While the gas was continuously supplied into thereactor, thermal treatment was performed at 950° C. for 3 hours. Theresulting product was left for about 4 hours, thereby obtaining poroussilicon composite primary particles. The porous silicon compositeprimary particles had a structure including needle-like silicon.

Comparative Preparation Example 2

A silicon-containing composite was prepared in the same manner as inPreparation Example 1, except that CH₄ was used as the reaction gas andpyridine was used as a N precursor.

When prepared according to Comparative Preparation Example 2, theadhesion of a silicon/silicon suboxide and a first graphene, and/or theadhesion of a porous silicon composite secondary particle and a secondgraphene in the resulting porous silicon composite was very poor.

Example 1: Manufacture of Negative Electrode and Coin Full Cell

The silicon-containing composite of Preparation Example 1, graphite,lithium polyacrylate (Li-PAA), and deionized water as a solvent weremixed to prepare a slurry. A ratio of a mixture of the porous siliconcomposite of Preparation Example 1 and graphite, and lithiumpolyacrylate in the slurry was about 92:8 by weight on a solid contentbasis. A ratio of the silicon-containing composite of PreparationExample 1 to graphite in the mixture was about 1:12 by weight.

The slurry was applied to a copper (Cu) foil using a doctor blade toform a film having a thickness of about 40 μm. The film was vacuum-driedat about 120° C. for about 2 hours and roll-pressed, therebymanufacturing a negative electrode.

A positive electrode was manufactured using a slurry obtained by mixingLiNi_(0.6)Co_(0.2)Mn_(0.2)O₂, Denka Black polyvinylidene fluoride (PVDF)as a binder, and NMP as a solvent. A mixed ratio by weight ofLiNi_(0.6)Co_(0.2)Mn_(0.2)O₂, Denka Black, and PVDF as a binder, in theslurry was about 93:5:2.

A coin full cell was manufactured using the negative electrode and apositive electrode. The slurry was applied to an aluminum (Al) foilusing a doctor blade to form a film having a thickness of about 40 μm.The film was vacuum-dried at about 120° C. for about 2 hours androll-pressed, thereby manufacturing the positive electrode.

A polypropylene membrane (Cellgard 3510) was used as a separator, and anelectrolyte was used which included 1.3M LiPF₆ in a mixture of ethylenecarbonate (EC), diethyl carbonate (DEC), and fluoroethylene carbonate(FEC) at a volume ratio of about 50:25:25.

Example 1A: Manufacture of Negative Electrode and Coin Full Cell

A coin full cell was manufactured in the same manner as in Example 1,except that 1.3 M LiPF₆ EC:DEC:FEC (at a volume ratio of 68:25:7) wasused as the electrolyte.

Examples 2 to 8: Manufacture of Negative Electrode and Coin Full Cell

Negative electrodes and coin full cells were prepared in the same manneras in Example 1, except that the silicon-containing composites ofPreparation Examples 2 to 8 were used, respectively, instead of theporous silicon-containing composite of Preparation Example 1.

Example 7A

A coin full cell was manufactured in the same manner as in Example 7,except that 1.3 M LiPF₆ EC:DEC:FEC (at a volume ratio of 68:25:7) wasused as the electrolyte.

Example 7B

A coin full cell was manufactured in the same manner as in Example 7,except that 1.3 M LiPF₆ EC:DEC (at a volume ratio of 75:25) was used asthe electrolyte.

Example 8A

A coin full cell was manufactured in the same manner as in Example 8,except that 1.3 M LiPF₆ EC:DEC:FEC (at a volume ratio of 68:25:7) wasused as the electrolyte.

Example 9: Manufacture of Negative Electrode and Coin Half Cell

The porous silicon-containing composite of Preparation Example 1, carbonblack (KB600JD), AST9005 (AEKYUNG, Republic of Korea), and deionizedwater as a solvent were mixed to prepare a slurry. A ratio by weight ofthe mixture of the porous silicon-containing composite of PreparationExample 1, carbon black (KB600JD), and AST9005 (AEKYUNG, Republic ofKorea) was about 79:1:20 on a solid basis.

The slurry was applied to a Cu foil using a doctor blade to form a filmhaving a thickness of about 40 μm. The film was vacuum-dried at about120° C. for about 2 hours and roll-pressed, thereby manufacturing anegative electrode.

A coin half cell was manufactured using the negative electrode and alithium metal as a counter electrode.

A polypropylene membrane (Celgard 3510) was used as a separator, and anelectrolyte was used which included 1.3M LiPF₆ in a mixture of EC, DEC,and FEC at a volume ratio of about 2:6:2.

Examples 10 to 16: Manufacture of Negative Electrode and Coin Half Cell

Negative electrodes and coin half cells were manufactured in the samemanner as in Example 9, except that the silicon-containing composite ofPreparation Examples 2 to 8 were used, respectively, instead of thesilicon-containing composite of Preparation Example 1.

Example 17: Manufacture of Negative Electrode and Coin Full Cell

A negative electrode and a coin full cell were manufactured in the samemanner as in Example 1, except that carbon black (KB600JD), was usedinstead of graphite.

Example 18: Manufacture of Negative Electrode and Coin Full Cell

A negative electrode and a coin full cell were manufactured in the samemanner as in Example 1, except that the ratio by weight of the mixtureof the silicon containing composite of Preparation Example 1 andgraphite was changed from about 1:12 to about 1:99.

Example 19: Manufacture of Negative Electrode and Coin Full Cell

A negative electrode and a coin full cell were manufactured in the samemanner as in Example 1, except that the ratio by weight of the mixtureof the silicon-containing composite of Preparation Example 1 andgraphite was changed from about 1:12 to about 3:97.

Example 20: Manufacture of Negative Electrode and Coin Full Cell

A negative electrode and a coin full cell were manufactured in the samemanner as in Example 1, except that the ratio by weight of the mixtureof the silicon-containing composite of Preparation Example 1 andgraphite was changed from about 1:12 to about 1:1.

Comparative Example 1: Manufacture of Negative Electrode and Coin FullCell

A negative electrode and a coin full cell were manufactured in the samemanner as in Example 1, except that the silicon composite primaryparticles of Comparative Preparation Example 1 were used instead of thesilicon-containing composite of Preparation Example 1.

Comparative Example 1A: Manufacture of Negative Electrode and Coin HalfCell

A negative electrode and a coin half cell were manufactured in the samemanner as in Example 9, except that the silicon-containing compositeprimary particles of Comparative Preparation Example 1 were used insteadof the silicon-containing composite of Preparation Example 1.

Comparative Example 2: Manufacture of Negative Electrode and Coin FullCell

A negative electrode and a coin full cell were manufactured in the samemanner as in Example 1, except that the silicon-containing composite ofComparative Preparation Example 2 were used instead of thesilicon-containing composite of Preparation Example 1.

Comparative Example 2A: Manufacture of Negative Electrode and Coin HalfCell

A negative electrode and a coin half cell were manufactured in the samemanner as in Example 9, except that the silicon-containing composite ofComparative Preparation Example 2 were used instead of thesilicon-containing composite of Preparation Example 1.

Evaluation Example 1: Charge and Discharge Characteristics

(1) Measurement of Initial Efficiency, Rate Capability, CoulombicEfficiency, and Discharge Capacity

1) Examples 1 to 8 and Comparative Example 1

Charge and discharge characteristics of the coin full cells of Examples1 to 8 and Comparative Example 1 were evaluated according to thefollowing methods:

(Charge: 1.0 C/Cutoff: 4.2 V-0.01 C, Discharge: 1.0 C/Cutoff: 2.8 V)

The results of evaluating the charge and discharge characteristics areshown in Table 2.

TABLE 2 Initial efficiency Lifespan Lifespan (%) (@ 100 times)(%) (@ 300times)(%) Example 1 87.0 95.1 77.3 Example 2 89.1 90.5 — Example 3 87.891.2 — Example 4 88 90.8 — Example 5 86.3 93.1 — Example 6 88.1 91.4 —Example 7 87 — — Example 8 86.7 — — Comparative 67 — 45.1 Example 1

2) Examples 7A, 7B, and 8A and Comparative Example 1

Charge and discharge characteristics of the coin cells of Examples 7A,7B, 8A, and Comparative Example 1 were evaluated according to thefollowing methods at a temperature of 45° C.

(Charge: 1.0 C/Cutoff: 4.2 V-0.01 C, Discharge: 1.0 C/Cutoff: 2.8 V)

The results of evaluating the charge and discharge characteristics areshown in Table 3.

TABLE 3 Lifespan (@ 300 times)(%) Example 7A 79.6 Example 7B 88.3 (@ 150times) Example 8A 79.1 Comparative Example 1 45.1

Evaluation Example 2: Raman Analysis

The silicon-containing composite of Preparation Example 1 was analyzedby Raman analysis using a Raman 2010 Spectra (NT-MDT Development Co.)(Laser system: 473, 633, 785 nm, Lowest Raman shift: ˜50 cm⁻¹, andspatial resolution: about 500 nm).

The results obtained by Raman analysis for the silicon-containingcomposite of Preparation Example 1 are shown in FIG. 4 . The intensityratios of peak D to peak G of the silicon-containing composite ofPreparation Example 1 were analyzed based on the results of the Ramananalysis, and the results thereof are shown in Table 4.

Raman spectra of graphene exhibit peaks at 1,350 cm⁻¹, 1,580 cm⁻¹, and2,700 cm⁻¹, providing information about a thickness, crystallinity, anda charge doping state. The peak at 1,580 cm⁻¹ is a peak referred to as“G-mode” which is generated from a vibration mode, i.e., stretching ofcarbon-carbon bonds, and an energy of the G-mode is determined by adensity of excess charges doped by graphene. The peak at 2,700 cm⁻¹ is apeak referred to as “2D-mode,” which is useful in evaluating a thicknessof the graphene. The peak at 1,350 cm⁻¹ is a peak referred to as“D-mode,” which appears when there is a defect in a SP² crystallinestructure. A D/G intensity (Id/Ig) provides information aboutdisordering of crystals of the graphene.

TABLE 4 Id/Ig Preparation Example 1 1.20

Referring to Table 4, it was confirmed that the silicon-containingcomposite of Preparation Example 1 had improved crystallinity andquality of the graphene.

Evaluation Example 3: X-Ray Photoelectron Spectroscopy (XPS) Analysis(Oxygen and Carbon Amounts in Graphene)

1) The oxygen and carbon amounts of the silicon-containing composite ofPreparation Examples 1 to 8 were analyzed by XPS, and the analysisresults are shown in Table 5.

The XPS analysis was performed using a Quantum 2000 (PhysicalElectronics. Inc.) (acceleration voltage: 0.5 keV˜15 keV, 300 W, energyresolution: about 1.0 eV, and sputter rate: 0.1 nm/min).

TABLE 5 Carbon (%) Oxygen (%) Preparation Example 1 22.0 6.9 PreparationExample 2 23.0 5.5 Preparation Example 3 22.0 6.5 Preparation Example 420 7.3 Preparation Example 5 22 7.4 Preparation Example 6 23 6.3Preparation Example 7 22 6.9 Preparation Example 8 29 7.12

In Table 5, a carbon amount was determined based on the carbon amountcorresponding to C1s peaks, and an oxygen amount was determined based onthe oxygen amount corresponding to O1s peaks.

Evaluation Example 4: Scanning Electron Microscopy (SEM)

The silicon-containing composite of Preparation Example 1 was analyzedby SEM, and the results are shown in FIGS. 9A and 9B. The resultsobtained by SEM analysis for the silicon-containing composite ofReference Preparation Example 1 are shown in FIGS. 10A and 10B.

Referring to FIGS. 9A, 9B, 10A, and 10B, it was confirmed that thesilicon-containing composite of Preparation Example 1 had excellentadhesion between the core and the shell and excellent coating uniformityof small-sized graphene, as compared with the silicon-containingcomposite of Reference Preparation Example 1.

Evaluation Example 5: Thermogravimetric Analysis (TGA)

The silicon-containing composite of Preparation Example 1 and ReferencePreparation Example 1 were subjected to TGA, and the results are shownin FIG. 5 .

Referring to FIG. 5 , it was confirmed that the silicon-containingcomposite of Example 1 had a 20 weight % loss temperature of about 720°C., which was reduced in the silicon-containing composite of ReferencePreparation Example 1 (20 weight % loss temperature of about 708° C.),resulting in improved thermal stability. In addition, it was observedthat the TGA derivative peak position was shifted toward a highertemperature.

Evaluation Example 6: Direct-Current Internal Resistance (DCIR)Characteristics 1) Examples 1 to 8 and Comparative Example 1

The resistance characteristics of the coin full cells of Example 1 andComparative Example 1 were measured after the 1^(st) and 100^(th)charging and discharging cycles according to the following method.

Each coin full cell was charged with a constant current of 0.1 C at atemperature of 25° C. until a voltage thereof reached 4.30 V (vs. Li),and maintained at a constant voltage mode until a current thereofreached a cut-off current of 0.05 C. Then, each coin full cell wasdischarged with a constant current of 0.1 C until a voltage thereofreached 2.8 V (vs. Li) (formation process, 1^(st) cycle). Such acharging and discharging cycle was performed two more times to completethe formation process.

Each coin full cell was charged with a constant current of 0.1 C (0.38mA/cm²) at a temperature of 25° C. until a voltage thereof reached 4.30V (vs. Li), and maintained at a constant voltage mode until a currentthereof reached a cut-off current of 0.05 C (2^(nd) Cycle).

The full cell was charged with a constant current of 1.0 C at atemperature of 25° C. until a voltage thereof reached 4.30 V (vs. Li),and maintained at a constant voltage mode until a current thereofreached a cut-off current of 0.01 C. Then, each coin full cell wasdischarged with a constant current of 1.0 C until a voltage thereofreached 2.8 V (vs. Li) (3^(st) Cycle). Such a charging and dischargingcycle was repeatedly performed (100^(th) Cycle).

As such, following the charging and discharging cycle, the impedance ofeach coin full cell was evaluated by measuring resistance according to a2-probe method using an impedance analyzer (Solartron 1260AImpedance/Gain-Phase Analyzer) at a temperature of 25° C. and in afrequency range of about 10⁶ megahertz (MHz) to about 0.1 MHz at avoltage bias of about 10 millivolts (mV). Accordingly, following the1^(st) charging and discharging cycle, DCIR of each coin full cell wasevaluated. The DCIR increase rate was calculated according to Equation1, and the results of the evaluation are shown in Table 6:DCIR increase rate (%)={(DCIR after 100^(th) cycle)/(DCIR after 1^(st)cycle)}×100%  Equation 2

Accordingly, the coin full cell of Example 1 was found to have a reducedDCIR increase rate as compared with that of Comparative Example 1.

TABLE 6 DCIR increase rate (%) Example 1 9.7 Example 7 20.0 Example 820.5 Comparative Example 1 21.1

Referring to Table 6, it was confirmed that the coin full cells ofExamples 1, 7, and 8 each had a reduced DCIR increase rate as comparedwith the coin full cell of Comparative Example 1.

2) Examples 7A, 7B, and 8A, and Comparative Example 1

The resistance characteristics of the coin full cells of Examples 7A,7B, and 8A, and Comparative Example 1 were measured after the 1^(st) and100^(th) charging and discharging cycles according to the followingmethod.

Each coin full cell was charged with a constant current of 0.1 C at atemperature of 25° C. until a voltage thereof reached 4.30 V (vs. Li),and maintained at a constant voltage mode until a current thereofreached a cut-off current of 0.05 C. Then, each coin full cell wasdischarged with a constant current of 0.1 C until a voltage thereofreached 2.8 V (vs. Li) (formation process, 1^(st) cycle). Such acharging and discharging cycle was performed two more times to completethe formation process.

Each coin full cell was charged with a constant current of 0.1 C (0.38mA/cm²) at a temperature of 25° C. until a voltage thereof reached 4.30V (vs. Li), and maintained at a constant voltage mode until a currentthereof reached a cut-off current of 0.05 C (2^(nd) Cycle).

The coin full cell was charged with a constant current of 1.0 C at atemperature of 25° C. until a voltage thereof reached 4.30 V (vs. Li),and maintained at a constant voltage mode until a current thereofreached a cut-off current of 0.01 C. Then, each coin full cell wasdischarged with a constant current of 1.0 C until a voltage thereofreached 2.8 V (vs. Li) (3^(st) Cycle). Such a charging and dischargingcycle was repeatedly performed (100^(th) Cycle).

As such, following the charging and discharging cycle, the impedance ofeach coin full cell was evaluated by measuring resistance according to a2-probe method using an impedance analyzer (Solartron 1260AImpedance/Gain-Phase Analyzer) at a temperature of 25° C. and in afrequency range of about 10⁶ MHz to about 0.1 MHz at a voltage bias ofabout 10 millivolts (mV). Accordingly, following the 1^(st) charging anddischarging cycle, DCIR of each coin full cell was evaluated. The DCIRincrease rate was calculated according to Equation 2, and the results ofthe evaluation are shown in Table 7:DCIR increase rate (%)={(DCIR after 100^(th) cycle)/(DCIR after 1^(st)cycle)}×100%  Equation 2

Accordingly, the coin full cells of Examples 7A, 7B, and 8A were foundto have a reduced DCIR increase rate as compared with that ofComparative Example 1.

TABLE 7 DCIR increase rate (%) Example 7a 10.5 Example 7b 1.5 Example 8a5 Comparative Example 1 21

Evaluation Example 7: Rate Capability

Each of the coin full cells of Example 1, 7, and 8 and ComparativeExample 1 was charged with a constant current of 0.1 C at a temperatureof 45° C. until a voltage thereof reached 4.30 V (vs. Li), andmaintained at a constant voltage mode until a current thereof reached acut-off current of 0.05 C. Then, each coin full cell was discharged witha constant current of 0.1 C until a voltage thereof reached 2.8 V (vs.Li) (formation process, 1^(st) cycle). Such a charging and dischargingcycle was performed two more times to complete the formation process.

Each coin full cell was charged with a constant current of 0.1 C (0.38mA/cm²) at a temperature of 25° C. until a voltage thereof reached 4.40V (vs. Li), and maintained at a constant voltage mode until a currentthereof reached a cut-off current of 0.05 C (2^(nd) Cycle).

The full cell was charged with a constant current of 0.5 C at atemperature of 25° C. until a voltage thereof reached 4.30 V (vs. Li),and maintained at a constant voltage mode until a current thereofreached a cut-off current of 0.01 C. Then, each coin full cell wasdischarged with a constant current of 0.5 C until a voltage thereofreached 2.8 V (vs. Li) (3^(st) Cycle).

The full cell was charged with a constant current of 1.0 C at atemperature of 25° C. until a voltage thereof reached 4.30 V (vs. Li),and maintained at a constant voltage mode until a current thereofreached a cut-off current of 0.01 C. Then, each coin full cell wasdischarged with a constant current of 1.0 C until a voltage thereofreached 2.8 V (vs. Li) (4^(st) Cycle).

And a stopping time of 10 minutes after one charge/discharge cycle inall of the above charge/discharge cycles.

The rate capability of each coin full cell is defined by Equation 3:Rate capability [%]=(Discharge capacity when a cell is discharged at arate of 1 C in 3^(rd) cycle)/(discharge capacity when a cell isdischarged at a rate of 0.2 C in 2^(nd) cycle)×100%  Equation 3

The results of the evaluation are shown in Table 8.

TABLE 8 Rate capability (1 C/0.2 C) Example 1 95.3 Example 7 98.9Example 8 96.3 Comparative Example 1 93.9

Accordingly, it was confirmed that the coin full cells of Examples 1, 7,and 8 had improved rate capability characteristics as compared with thecoin full cell of Comparative Example 1.

Evaluation Example 8: XPS Analysis (C/Si Amount)

The silicon-containing composites of Preparation Example 1 and ReferencePreparation Example 1 were analyzed by XPS.

Quantitative analysis of amounts of carbon and silicon atoms in eachsample was performed using XPS analysis. When a photon (X-ray) having acertain energy is irradiated on a sample, photoelectrons are emittedfrom the sample. When the kinetic energy of the photoelectrons ismeasured, a binding energy required for emitting the photoelectrons maybe determined. Since such a binding energy is an intrinsic property ofan atom, elemental analysis and measurement of the surface concentrationof the element may be possibly performed. Based on the quantitativelyanalyzed amounts of carbon and silicon atoms, a C/Si amount may becalculated.

The XPS analysis was performed using a Quantum 2000 (PhysicalElectronics. Inc.) (acceleration voltage: 0.5 keV˜15 keV, 300 W, energyresolution: about 1.0 eV, minimal analysis area: 10 micro, and sputterrate: 0.1 nm/min).

After each sample was vacuum dried at a temperature of 110° C. for 12hours, each sample was transferred to a preliminary chamber of the XPSspectrometer.

The chamber was then subjected to degasification at a temperature of 25°C. in a vacuum of about 10⁻⁴ torr to about 10⁻⁵ torr. Then, each samplewas transferred into the analysis chamber and measured when thebackground vacuum was on the order of 10⁻¹⁰ torr.

Here, peaks with a binding energy of about 98 eV to about 105 eV belongto Si2p, and peaks with a binding energy of about 282 eV to about 297 eVbelong to c1s.

As a ratio of the integral value of these peaks, the C/Si amount wascalculated. Among the results of the XPS analysis, peaks belonging toC1s, Si2p, and N1s are each shown in FIGS. 6 to 8 , and the C/Si amountand each element amount are shown in Table 9.

TABLE 9 C/Si Atomic % (atomic ratio) C1s Si2p N1s O1s Preparation 161.3498.42 0.61 0.15 0.82 Example 1 Reference 29.9 94.48 3.15 0 2.37Preparation Example 1

Referring to Table 9, the silicon-containing composite of PreparationExample 1 was found to have a significantly increased C/Si amount, ascompared with that of Reference Preparation Example 1. Accordingly, itwas confirmed that the silicon-containing composite of PreparationExample 1 had better adhesion between silicon/silicon suboxide andgraphene and better coating uniformity of graphene, as compared withthat of Reference Preparation Example 1.

Evaluation Example 9: Transmission Electron Microscopy (TEM)

The silicon-containing composite of Preparation Example 1 was analyzedby TEM using a Titan cubed G2 60-300 (FEI).

The resulting TEM images of the silicon-containing composite ofPreparation Example 1 are shown in FIGS. 11A and 11B.

Referring to FIGS. 11A and 11B, it was confirmed that thesilicon-containing composite of Preparation Example 1 had good adhesionbetween silicon/silicon oxide and graphene and good coating uniformityof graphene over the silicon/silicon oxide.

As shown in FIG. 11A, the first graphene and the second graphene werefound to be oriented at an angle of about 90° with respect to a majoraxis (Y-axis) of the silicon suboxide film (SiO_(x), wherein 0<x<2)formed on the surface of the plate- and needle-like silicon particles.

As described above, according to an embodiment, when used as anelectrode active material, a silicon-containing composite may form anetwork between silicon particles to thus suppress expansion of anelectrode plate during charging and discharging, and may improve theinitial efficiency and volume energy density of a lithium battery. Thesilicon-containing composite may also form a conductive and durableprotective layer for silicon, and thus may improve durability of thelithium battery against charging and discharging.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould be considered as available for other similar features or aspectsin other embodiments.

While one or more embodiments have been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A silicon-containing composite comprising: aporous core comprising a porous silicon composite secondary particle;and a shell on a surface of the porous core and surrounding the porouscore, wherein the porous silicon composite secondary particle comprisesan aggregate of silicon composite primary particles, each comprisingsilicon, a silicon suboxide on a surface of the silicon, and a firstgraphene on a surface of the silicon suboxide, wherein the shellcomprises a second graphene, and wherein at least one of the firstgraphene and the second graphene comprises at least one element selectedfrom nitrogen, phosphorus, and sulfur, wherein a thickness of thesilicon suboxide is about 0.1 nanometer to less than 1 nanometer, andwherein the first graphene comprises a plurality of layers and thenumber of graphene layers in the first graphene of the core is identicalto or different from the number of graphene layers in the secondgraphene of the shell, and the second graphene of the shell has adensity which is greater than a density of the first graphene of thecore.
 2. The silicon-containing composite of claim 1, wherein thesilicon suboxide is present in a form of a film, a matrix, or acombination thereof, and the first graphene and the second graphene areeach independently in a form of a film, a particle, a matrix, or acombination thereof.
 3. The silicon-containing composite of claim 1,wherein the first graphene is disposed directly on the surface of thesilicon suboxide, and the second graphene is disposed directly on thesurface of the silicon composite secondary particle.
 4. Thesilicon-containing composite of claim 1, wherein an amount of the atleast one element selected from nitrogen, phosphorus, and sulfur in thesilicon-containing composite is about 0.2 atomic percent or less at asurface depth of 10 nanometers or less, as analyzed by X-rayphotoelectron spectroscopy.
 5. The silicon-containing composite of claim1, wherein a carbon to silicon atomic ratio in the silicon-containingcomposite is from about 100:1 to about 200:1, when analyzed by X-rayphotoelectron spectroscopy, and wherein the carbon to silicon atomicratio is increased as compared with the carbon to silicon atomic ratioin a silicon-containing composite which does not comprise the at leastone element selected from nitrogen, phosphorous, and sulfur.
 6. Thesilicon-containing composite of claim 1, wherein an intensity ratio ofpeak D to peak Gin the silicon-containing composite is about 0.8 toabout 1.5, when analyzed by Raman spectroscopy.
 7. Thesilicon-containing composite of claim 1, wherein as measured bythermogravimetric analysis, a 20% weight loss temperature of thesilicon-containing composite is about 7° C. to about 15° C. greater thana 20% weight loss temperature of a silicon-containing composite whichdoes not comprise the at least one element selected from nitrogen,phosphorous, and sulfur.
 8. The silicon-containing composite of claim 1,wherein the silicon-containing composite comprises a first core/shellstructure and a second core/shell structure.
 9. The silicon-containingcomposite of claim 1, wherein the first core/shell structure comprisesthe porous core comprising the porous silicon composite secondaryparticle and the shell comprising the second graphene on the surface ofthe porous core, and the second core/shell structure comprises a corecomprising the silicon and the silicon suboxide on a surface of thesilicon, and the shell comprises the first graphene on a surface of thesilicon suboxide.
 10. The silicon-containing composite of claim 1,wherein the total amount of the first graphene and the second grapheneis from about 0.1 parts by weight to about 2,000 parts by weight basedon 100 parts by weight of silicon.
 11. The silicon-containing compositeof claim 1, wherein the first graphene of the silicon composite primaryparticle is spaced apart from a surface of the silicon suboxide by adistance of about 10 nanometers or less, and the first graphene isoriented at an angle of about 0° to about 90° with respect to a majoraxis of the silicon.
 12. The silicon-containing composite of claim 1,wherein the first graphene comprises about 1 to about 30 graphenelayers, and has a total thickness of about 0.3 nanometers to about 1,000nanometers.
 13. The silicon-containing composite of claim 1, wherein thesecond graphene of the shell is spaced apart from the silicon suboxideby a distance of about 1,000 nanometers or less, and the second grapheneis oriented at an angle of about 0° to about 90° with respect to a majoraxis of the silicon.
 14. The silicon-containing composite of claim 1,where the second graphene comprises about 1 to about 30 graphene layers,and has a total thickness of about 0.6 nanometers to about 50nanometers.
 15. The silicon-containing composite of claim 1, wherein thesilicon has a form comprising a sphere, a nanowire, a needle, a rod, aparticle, a nanotube, a nanorod, a wafer, a nanoribbon, or a combinationcomprising at least one of the foregoing.
 16. The silicon-containingcomposite of claim 1, wherein the porous silicon composite secondaryparticle has an average particle diameter of about 1 micrometer to about30 micrometers, a specific surface area of about 0.1 square meter pergram to about 100 square meters per gram, and a density of about 0.1gram per cubic centimeter to about 2.57 grams per cubic centimeter. 17.The silicon-containing composite of claim 1, wherein the silicon has anaverage particle diameter of about 10 nanometers to about 30micrometers.
 18. The silicon-containing composite of claim 1, wherein anamount of oxygen in the silicon-containing composite is from about 0.01atomic percent to about 15 atomic percent based on the total atomicpercentage of oxygen, carbon, and silicon atoms in thesilicon-containing composite.
 19. The silicon-containing composite ofclaim 1, further comprising a carbonaceous coating layer on a surface ofthe silicon-containing composite, the carbonaceous coating layercomprising an amorphous carbon.
 20. The silicon-containing composite ofclaim 19, wherein the carbonaceous coating layer further comprises atleast one element selected from nitrogen, phosphorous, and sulfur. 21.The silicon-containing composite of claim 19, wherein the carbonaceouscoating layer further comprises a crystalline carbon.
 22. Thesilicon-containing composite of claim 19, wherein the carbonaceouscoating layer is a non-porous continuous coating layer, and has athickness of about 1 nanometer to about 5,000 nanometers.
 23. A methodof preparing the silicon-containing composite of claim 1, the methodcomprising: providing a porous silicon composite secondary particle;supplying at least one of a nitrogen precursor, a phosphorus precursor,or a sulfur precursor, and a gas comprising a carbon source, to theporous silicon composite secondary particle to form a supplied poroussilicon composite secondary particle; and thermally treating thesupplied porous silicon composite secondary particle to form the shellon the porous silicon composite secondary particle and prepare thesilicon-containing composite.
 24. The method of claim 23, wherein thethermally treating comprises reacting the porous silicon compositesecondary particle with the carbon source and the at least one of thenitrogen precursor, the phosphorus precursor, or the sulfur precursor.25. The method of claim 23, wherein the providing of the porous siliconcomposite secondary particle comprises preparing a compositioncomprising a dispersing agent, a first solvent, and particles comprisingsilicon and silicon suboxide on a surface of the particle comprisingsilicon.
 26. The method of claim 25, wherein the first solvent comprisesan alcohol, and wherein the providing of the porous silicon compositesecondary particle comprises spray-drying the composition.
 27. Themethod of claim 25, wherein the dispersing agent comprises stearic acid,resorcinol, polyvinyl alcohol, carbon pitch, or a combination thereof.28. The method of claim 23, wherein the nitrogen precursor is ammonia.29. The method of claim 23, wherein the carbon source comprises acompound represented by Formula 1, a compound represented by Formula 2,an oxygen-containing compound represented by Formula 3, or a combinationthereof:C_(n)H_((2n+2−a))[OH]_(a)  [Formula 1] wherein, in Formula 1, n is aninteger of 1 to 20, and a is 0 or 1,C_(n)H_((2n))  [Formula 2] wherein, in Formula 2, n is an integer of 2to 6, and/orC_(x)H_(y)O_(z)  [Formula 3] wherein, in Formula 3, x is an integer of 1to 20, y is 0 or an integer of 1 to 20, and z is 1 or
 2. 30. The methodof claim 29, wherein the carbon source gas comprising a carbon sourcefurther comprises a first oxygen-containing compound represented byFormula 3a, which is different from the oxygen-containing compound ofFormula 3;C_(x)H_(y)O_(z)  [Formula 3] wherein, in Formula 3a, x is 0 or aninteger of 1 to 20, y is 0 or an integer of 1 to 20, and z is 1 or 2.31. The method of claim 23, wherein the gas comprising a carbon sourcecomprises methane, ethylene, propylene, acetylene, methanol, ethanol,propanol, or a combination thereof.
 32. The method of claim 23, whereinan amount of the at least one of the nitrogen precursor, the sulfurprecursor, or the phosphorus precursor is about 20 volume percent orless based on the total volume of the gas comprising a carbon source andthe at least one of the nitrogen precursor, the sulfur precursor, or thephosphorus precursor.
 33. The method of claim 23, wherein the thermallytreating is performed at a temperature of about 750° C. to about 1,100°C.
 34. The method of claim 23, further comprising dry-blending a mixturecomprising the porous silicon composite secondary particle, acarbonaceous material, and a solvent to obtain a coated poroussilicon-composite secondary particle comprising a carbonaceous coatinglayer formed thereon.
 35. The method of claim 34, wherein the mixturefurther comprises at least one of the nitrogen precursor, the sulfurprecursor, or the phosphorus precursor.
 36. The method of claim 34,further comprising reacting the coated porous silicon compositesecondary particle comprising the carbonaceous coating layer with atleast one of the nitrogen precursor, the sulfur precursor, and thephosphorus precursor.
 37. A carbon composite comprising thesilicon-containing composite of claim 1 and a carbonaceous material. 38.The carbon composite of claim 37, wherein an amount of the carbonaceousmaterial is about 0.001 part by weight to about 99 parts by weight basedon 100 parts by weight of the carbon composite.
 39. An electrodecomprising the silicon-containing composite of claim 1, a carboncomposite comprising the silicon-containing composite of claim 1 and acarbonaceous material, or a combination thereof.
 40. The electrode ofclaim 39, wherein the carbonaceous material comprises graphene,graphite, fullerene, graphitic carbon, carbon fiber, carbon nanotube, ora combination thereof, and an amount of the carbonaceous material isabout 0.001 part by weight to about 99.999 parts by weight based on 100parts by weight of the carbon composite.
 41. A lithium batterycomprising the electrode of claim
 39. 42. A device comprising thesilicon-containing composite of claim 1, a carbon composite comprisingthe silicon-containing composite and a carbonaceous material, or acombination thereof.
 43. The device of claim 42, wherein the device is afield emission device, a biosensor, a semiconductor device, or athermoelectric device.
 44. The silicon-containing composite of claim 1,wherein the first graphene comprises at least one element selected fromnitrogen, phosphorus, and sulfur.
 45. A silicon-containing compositecomprising: a core comprising a porous silicon composite secondaryparticle; and a shell on and surrounding the core, wherein the poroussilicon composite secondary particle comprises an aggregate of siliconcomposite primary particles, each comprising a silicon suboxide, athermal treatment product of the silicon suboxide, or a combinationthereof; and a first graphene on a surface of the silicon suboxide, thethermal treatment product of the silicon suboxide, or the combinationthereof, wherein the shell comprises a second graphene, and at least oneof the first graphene and the second graphene comprises at least oneelement selected from nitrogen, phosphorus, and sulfur, wherein athickness of the silicon suboxide is about 0.1 nanometer to less than 1nanometer, and wherein the first graphene comprises a plurality oflayers and the number of graphene layers in the first graphene of thecore is identical to or different from the number of graphene layers inthe second graphene of the shell, and the second graphene of the shellhas a density which is greater than a density of the first graphene ofthe core.
 46. The silicon-containing composite of claim 45, wherein thethermal treatment product of the silicon suboxide is obtained bythermally treating the silicon suboxide in an atmosphere comprising acarbon source gas or a combination of a carbon source gas and a reducinggas.
 47. The silicon-containing composite of claim 45, wherein thethermal treatment product of the silicon suboxide has a structurecomprising silicon arranged in a matrix of SiO_(y), wherein 0<y≤2. 48.The silicon-containing composite of claim 45, wherein the thermaltreatment product of the silicon suboxide comprises: a structurecomprising silicon in a matrix of SiO₂, a structure comprising siliconin a matrix comprising SiO₂ and SiO_(y), wherein 0<y<2, or a structurecomprising silicon in a matrix of SiO_(y), wherein 0<y<2.
 49. Thesilicon-containing composite of claim 45, wherein the first graphenecomprises at least one element selected from nitrogen, phosphorus, andsulfur.